"gigantopterid" = an English noun describing large leaves with complex reticulate venation resembling the Cathaysian fossil seed plant genus Gigantopteris and North American genus Delnortea of the Permian Period, 260 million years ago"

You are here: Evolution of Mesozoic Angiosperms

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[ Evolution of Mesozoic Angiosperms ]

JOHN M. MILLER, Ph.D.

University and Jepson Herbaria
Room 1001, Valley Life Sciences Building 2465
University of California, Berkeley
Berkeley, California, USA 94720-2465



Evolution of stem- and crown-group flowering plants is discussed from molecular-systematic-, floral tool kit-, and paleobotanical research perspectives in this third of three essays on the origin of angiosperms. I also bring back to life monocotyledonous elements of a ghost lineage of flowering plants traced from Norian sanmiguelias. Middle Triassic magnoliid palynofloras of arid, boreal, and tropical paleoenvironments are also discussed. There is little doubt that Bayesian computational molecular-clock simulations by Beaulieu et al. (2015) predict angiosperm occurrences in Anisian times and places, which are supported by Hochuli and Feist-Burkhardt palynological data (2004, 2013).

Paleoecologies of these ancient stem-group angiosperm populations were not "dark and disturbed," or "wet and wild," or explainable by any other nonsensical and sophomoric pairing of adjectives. I also review the literature on the basic biology and molecular evolution of extant basal angiosperms as defined by The Angiosperm Phylogeny Group (APG IV 2016) to include enigmatic monocotyledonous Hydatellaceae (Friis and Crane 2007, Rudall et al. 2009, Sokoloff et al. 2009, M. L. Taylor et al. 2010, Prychid et al. 2011, Kynast et al. 2014).

Rothwell and Stockey (2016) and Rothwell et al. (2009) are probably better working seed plant phylogenies than those proposed by J. A. Doyle (2008), among others, or discussed by Cascales-Miñana et al. (2016).

The slab pictured to the left was unearthed from the Lower Cretaceous Dakota Formation of North America. The rock contains an indeterminate eudicot fossil flower. Specimen IU15713-3429 was first photographed by the author in 1981 with the permission of Professor David L. Dilcher. The same specimen was illustrated in Figure 1 [as "D"] on Page 512 of J. F. Basinger and D. L. Dilcher (1984), Ancient bisexual flowers, Science 224: 511-513.

Despite considerable discussion in the literature on angiosperm phylogeny and evolution by M. W. Chase, J. A. Doyle, E. M. Friis, M. W. Frohlich, D. E. Soltis, and P. S. Soltis, among others, Caytoniales, Corystospermales, or Petriellales probably had nothing to do with the "mysterious origin of flowering plants" (this phrase is quoted from page 1074, Discussion, Ecology and Paleoenvironment, Bomfleur et al. 2014).

Simply put, cone and floral tool kits are too conserved i.e. demonstrably Permo-carboniferous in origin to somehow accommodate bizarre morphologies seen in Mesozoic Caytoniales. Further, there is simply no evidence of a transitional series or chronocline leading from Caytoniales to the Amborellanae, Austrobaileyanae, Nymphaeanae, and Magnolianae.

This line of paleobiological thinking obviates ideas on a proclaimed recent origin of the flower (Glover 2014, Chanderbali et al. 2016). Simply put, the angiosperm flower is a deeply-conserved organ with a body plan seen in several Paleozoic seed plant fossils including species of Vojnovskyales, among others yet to be confirmed by sophisticated paleobotanical studies.

A Mesozoic radiation of angiosperms is cast within the framework of the Angiosperm Phylogeny Group proposed classification (APG III 2009, Chase and Reveal 2009, APG IV 2016). Two books dealing with the subject of angiosperm evolution (Dilcher 2010, Friis et al. 2011) were also consulted.

The previous essay raises the possibility that flowering plants might be an amalgam of paraphyletic evolutionary lines traceable to surviving geographically disparate early Triassic remnants of already divergent Permian seed plant lineages. This idea is supported by reanalysis of nucleic acid data suggesting a late Triassic age for the flowering plant crown group (Stephen A. Smith et al. 2010).

Molecular-phylogenetic analyses by Magallón (page 395, 2010) when calibrated with fossil data and compared with different relaxed clock methods "... imply that the diversification that lead to living angiosperm species began sometime between the Upper Triassic and the early Permian." Rate Scenario 3 depicted in Figure 4 on page 874 of Beaulieu et al. (2015) is particularly intriguing.

Students have ample opportunities to compare and contrast Bayesian relaxed-clock methods and to discuss Yule birth-death priors when comparing angiosperm and seed plant phylogenies computed by Bell et al. (2005, 2010), Stephen A. Smith et al. (2010), Magallón (2010, 2014), and Magallón et al. (2015), among others, with the Professor Charles Marshall analyses (Condamine et al. 2015).

Appropriate choice of priors during the course of Bayesian molecular-clock simulations affects estimates on the age of cycad clade branches (Condamine et al. 2015). Birth-death priors, when used in molecular-phylogenetic simulations are more congruent with the fossil record of ancient groups (older-diverging clades) than Yule techniques, and this observation holds true for other biological groups (Condamine et al. 2015) including monocotyledonous flowering plants (Eguchi and Tamura 2016).

Was Triassic Pangaea a "world devoid of angiosperms" (page 295, Conclusions, Labandeira 2014). No, according to Cornet (1986, 1989, 1993), Zavada (2007), and Hochuli and Feist-Burkhardt (2004, 2013).

Paleobotanical data (Cornet 1986, 1989, Cornet and Habib 1992, Cornet 1993), which are challenged and marginalized by certain colleagues, are concordant with some of the mathematical predictions and spin-offs from simulations published by Stephen A. Smith et al. (2010) and Beaulieu et al. (2015).

Joinvilleaceae are monocotyledonous flowering plants (Tomlinson and A. C. Smith 1970) that share vegetative morphology reminiscent of the enigmatic and controversial Triassic fossil Sanmiguelia lewisii.

A clump of Joinvillea plicata (Joinvilleaceae, Poales, Lilianae) indigenous to Viti Levu Island of the South Pacific Ocean is pictured to the right. The late Saula Vodonaivalu, Curator Emeritus of the South Pacific Regional Herbarium, University of the South Pacific, is standing next to the plant (photographed by the author).

Based on gene expression studies of extant angiosperm species does the foliar morphology, stem anatomy, and growth habit of Sanmiguelia lewisii display the fingerprint of an "ancestral developmental tool kit" (title, Floyd and Bowman 2007) of a monocotyledonous flowering plant? Yes.

Definitive paleontological evidence published by Peter Hochuli and Susanne Feist-Burkhardt should be read together with a 2013 Sidney Ash and Hasiotis review of Sanmiguelia paleobiology, and their report of three new localities from the Blue Mesa Member (Norian) of the Lower Triassic Chinle Formation of southwestern North America.

The fossil record of flowering plants is grossly incomplete despite an optimistic appraisal by Friis et al. (2011). Every one of the simulations computed by Beaulieu et al. (2015) suggest a Triassic age for angiosperms, which is consistent with a growing body of paleontological evidence. More field- and laboratory work is needed with focus on rock layers Permo-triassic in age to find and describe fossils of reproductive spur- [short-] shoots, and detached and shed angiospermous organs and foliar remains.

"... Prevailing hypotheses, based on evidence both from living and from fossil plants, emphasize that the earliest angiosperms were plants of small stature with rapid life cycles that exploited disturbed habitats in open or perhaps understorey conditions ..."

The preceding statement is quoted from the abstract of a letter on page 551 of E. M. Friis, P. R. Crane, K. R. Pedersen, M. Stampanoni, and F. Marone (2015), Exceptional preservation of tiny embryos documents seed dormancy in early angiosperms, Nature 528: 551-554.

Magallón et al. (2015) excluded the Triassic fossil Sanmiguelia lewisii (see the blue-bars on Figure 1) from the angiosperm molecular-phylogenetic analysis, ignoring possibly severe repercussions on calibration of the angiosperm radiation.

Phylogenomics suggests Cretaceous co-radiations of Diptera, Hymenoptera, and Lepidoptera, and angiosperms. A milestone research report on the molecular systematics of insect nuclear genes by Misof et al. (2014) suggest Early Cretaceous "spectacular diversifications" of ants, bees, butterflies, moths, flies, and wasps with "the radiation of flowering plants."

Yet, there are incongruencies in a milestone phylogenomic analysis of 1468 single-copy insect nuclear genes by the Bernhard Misof team (2014) with reanalyses of the data by K. Jun Tong et al. (2015) employing Bayesian priors and fine-tuning node calibrations with fossils, which parallel problems with competing analyses of seed plant molecular data sets discussed by Beaulieu et al. (2015), Condamine et al. (2015), and Magallón et al. (2015), especially when paleontological considerations are included in tree-thinking.

"... we estimate the ages of the megadiverse orders Diptera [flies] and Lepidoptera [butterflies and moths] at ≈266 and ≈263 Ma [million years ago], respectively. These are ≈100 My [million years] earlier than those of Misof et al. [2014]. Our estimates are consistent with the fossil record ... and challenge the hypothesis that these two orders diversified contemporaneously with angiosperms" (quoted from K. Jun Tong et al. 2015, words in brackets [] are mine).

A review of Cretaceous records for clumped angiosperm pollen and its bearing on coevolution with insect pollinators is available (D. W. Taylor et al. 2010).

By reviewing the vast literature on tool kit evo-devo, and through incorporation of molecular-phylogenetic studies by Beaulieu, Chase, Donoghue, Mathews, Savard, and Stephen A. Smith, among others, coupled with modeling of the alpha (α)- swarm of WGDs by Jiao and colleagues, I have reached a surprising conclusion that intergeneric hybrids between Permo-carboniferous gigantopteroids including Delnortea abbottiae and Evolsonia texana, and species of Vojnovskyales constitute the allopolyploid ancestors of angiosperms.

Studies of the "angiosperm history" and the genome landscape of the poster-boy [-girl] basal angiosperm Amborella trichopoda (Amborellaceae, Amborellales, Amborellanae) are probably unhelpful in deciphering the paleobiology of Permo-carboniferous seed plant groups modeled by Jiao et al. (2011).

The next chapter discusses the fossil history and evolution of Mesozoic angiosperms. The numbering of tables in this chapter follows Table 5, Anthophytes, Conifers, and Gigantopteroids without Core Pteridosperms: Character Data Matrix Process ANTHO, which is located near the end of the previous essay on the Paleobotany of Angiosperm Origins.


Stem Group Flowering Plants:

Flowering plants are the most successful group of land plants on Earth. According to a review by Crepet and Niklas (page 368, 2009), ideas on the diversification and success of angiosperms "fall into one of three camps: ..."

  • hypotheses that focus on vegetative attributes such as diverse anatomy, phenotypic plasticity, rapid growth rates, and high hydraulic conductivity;
  • hypotheses on the adaptability and efficiency of reproductive modules such as floral display, pollination ecology, embryology, and fruit and seed dispersal and ecology; and
  • hypotheses that incorporate a discussion of innovative developmental tool kits (to confer plasticity) and elaborations of secondary biochemical pathways needed to manufacture natural plant products in the arsenal for the coevolutionary arms race.
  • A fourth, ecologically-grounded soil nutrient-feedback hypothesis is advanced by Berendse and Scheffer (2009).

    "Did insect pollination cause increased seed plant diversity?" (Gorelick 2001). These questions, among others (Berendse and Scheffer 2009, Crepet and Niklas 2009) should now be discussed from a late Paleozoic temporal perspective based on evidence presented in the first and second essays.

    Angiosperm ghost lineage. There is growing consensus among some molecular systematists and paleobotanists on the existence of a 160 million year old angiosperm ghost lineage rooted at the angiosperm-gymnosperm split roughly 300 MYA, prior to the end-Permian extinction. Calibrating the timing of this split together with the other Great Late Paleozoic Seed Plant Divergences, using guide fossils, will be important exercises in future combined molecular- and morphological-phylogenetic analyses.

    A possible paraphyletic Paleozoic origin of angiosperms contradicts proposals by Leebens-Mack et al. (2005) suggesting a monophyletic Mesozoic origin of a basal clade of flowering plants, which is based on estimates derived from cpDNA data.

    Employing refined methods to estimate rates of divergence of flowering plants, Charles Bell and colleagues (2010) publish a milestone paper based on more than 500 extant taxa and 35 calibration points.

    Ancestors of putative paraphyletic grades of angiosperms might have been Permo-Carboniferous or Permo-Triassic gymnosperms with hermaphroditic (bisexual) strobili.

    I also built a case and presented evidence in the second essay that some of the candidate gymnosperm groups with bisexual protoflowers are presently known only from detached taeniopteroid sporophylls and foliar tepals of Ginkgo-like spur shoots, and subtending gigantopteroid megaphylls. Permian delnorteas and evolsonias probably fit this bill but more paleobotanical field work is needed to match the detached pieces to the whole mother plant.

    The drawing to the right is Lesqueria elocata (family uncertain, Magnoliales, Magnolianae) from page 399 of Crane and Dilcher (1984), Lesqueria: an early angiosperm fruiting axis from the mid-Cretaceous, Annals of the Missouri Botanical Garden 71(2): 384-402, reproduced by permission from Peter Crane, David Dilcher, and the Missouri Botanical Garden.

    "Figure 47. Reconstruction of the Lesqueria elocata fruiting axis."

    This statement by Wing and Boucher (page 380, 1998) is probably incorrect: "Despite the singular ecological significance and species diversity of angiosperms, they are not in a genealogical sense one of the major branches of land plants and did not originate with other major land plant clades (e.g. lycopsids, ferns, conifers, cycads, ginkgos) during the middle or late Paleozoic."

    Feild and Arens (2007) are probably also on thin ice when asserting that flowering plants originated in specific terrestrial paleoenvironments during the earliest Cretaceous Period. Simply put, apparent absence of angiosperm fossils in the Triassic and Jurassic stratigraphic record is not data.

    Absence of paleobotanical data is not a substitute for fact when dealing with a probable ghost lineage due to insufficient sampling, especially in view of more than a dozen molecular phylogenetic studies pointing to ancient gene duplications and deep time divergences between angiosperms and its nearest relative (S. Kim et al. 2004, D. E. Soltis et al. 2007, Jiao et al. 2011).

    Floral tool kits are deeply conserved. Almost every molecular-phylogenetic study of DNA-binding seed plant transcription factors (TFs) suggests deep conservation of the cone and floral tool kit. This fact is congruent with Bayesian molecular-clock simulations computed by Beaulieu et al. (2015) supporting Triassic age estimates for flowering plants.

    Biochemical and morphological evidence suggests that cones and flowers are reproductive short shoots. If fertile spur shoots are demonstrably ancient organs known from late Paleozoic seed plant fossils then how could the flower possibly originate in the late Mesozoic? Strangely, Chanderbali and coworkers resuscitate this paradox (2016).

    Some of the high points on floral evo-devo of eudicots with bearing on the greater question of the timing of the origin of floral organs are published in recent works by Hileman and Irish (2009), Korotkova et al. (2009), Rasmussen et al. (2009), Endress (2010), C. Liu et al. (2010), Bharti Sharma et al. (2011), and Becker (2016). Peter Endress reviews the developmental morphology of the angiosperm carpel (2015).

    "While the amazing conservation of the major floral identity [ABCDE] program is being unravelled by analysing floral homeotic gene function and expression, we are only just beginning to understand the evolution of the gene network governing the organ identity genes ... " (Abstract Scope and Conclusions, page 145, Becker 2016, item in [brackets] is mine).

    Ongoing genomic studies (Chanderbali et al. 2008, Liang et al. 2011, Amborella Genome Project 2013, P. S. Soltis and D. E. Soltis 2013, among others), and APG IV (2016) might be unhelpful in understanding the angiosperm floral paradox.

    "Darwin himself referred to the 'early origin and diversification of angiosperms' as 'an abominable mystery,' and the origin of the flower- and therefore flowering plants- is still a question ..."

    The preceding statement is quoted from page 86 of Pamela S. Soltis and Douglas E. Soltis (2014), Chapter 4. Flower diversity and angiosperm diversification. Pp. 85-102 In: J. L. Riechmann and F. Wellmer (eds.), Flower Development: Methods and Protocols, Volume 1110. New York: Springer, 475 pp.

    Genomic studies of the cultivated grape overwhelmingly support paleohexaploidy (Jaillon et al. 2007), which is equivalent to the "γ triplication" cited by Jiao et al. (2011) that occurred in the common ancestor of eudicots and monocots.

    In terms of paleopolyploidy, one or more gene duplications in the APETALA3/PISTILLATA (AP3/PI) B-class MADS-box gene lineage might have paved the way for the evolutionary development of proanthostrobili 290 MYA (S. Kim et al. 2004). Genomic data on the timing of WGDs (Jiao et al. 2011) will require calibrating with well-dated guide fossils to be selected by paleontologists.

    Zhong-Jian Liu and Xin Wang published a controversial fossil find of a detached, single flower from the Malm (Middle to Upper Jurassic) of Asia in 2015. I discuss this discovery among others from the Xin Wang Laboratory and Nanjing Institute of Geology and Palaeontology elsewhere on this web site.

    The drawing to the left is Euanthus panii (family uncertain, order not yet assigned, Magnolianae). Artist's reconstruction is reproduced with the written permission of Xin Wang, Nanjing Institute of Geology and Palaeontology, copyright ©2015, all rights reserved.

    Despite possible problems with the chain of custody of this fossil, the purported place of collection including rock outcrops in the vicinity, have been dated using 40Ar/39 methods to constrain the supposed age of the Haifanggou and Lanqi formations (S-C. Chang et al. 2014).

    Studies of the emerging fossil record of possible angiosperms and other seed plants recovered from Asian rocks are reviewed by Xin Wang (2009, 2014).

    Vivian Irish (2006) provides a road map to diversification of the angiosperm clade from the perspective of evo-devo of floral homeotic genes, their phenotypic expression, and molecular phylogenies. This line of research is reviewed by Becker (2016).

    Most of the explosive radiation of floral diversity in basal lineages of flowering plants is explained by duplication and diversification of the MIKC-type MADS-box family of genes (P. S. Soltis et al. 2009, P. S. Soltis and D. E. Soltis 2016).

    "... the WGD [α-swarm or ε?] that preceded the origin of the angiosperms clearly provided genetic fodder that appears to have resulted in the key innovation we know as the flower [protoflower?] ..."

    The preceding statement is quoted from page 160 of P. S. Soltis and D. E. Soltis, (2016), Ancient WGD events as drivers of key innovations in angiosperms, Current Opinion in Plant Biology 30: 159-165, comments and symbols [in brackets] are mine.

    Ancestral floral bauplan. The many studies reviewed by J. A. Doyle and Endress (2000), Endress and J. A. Doyle (2009), Hileman and Irish (2009), Rasmussen et al. (2009), P. S. Soltis et al. (2009), Specht and Bartlett (2009), and Melzer et al. (2010) are a foundation for inferring the morphology of the ancestral angiosperm flower and determining the phylogenetic position of derived modern flowering plant groups.

    While discussing their perception of the flower "... and its initial evolutionary modifications ..." within the context of extant basal angiosperms, Endress and J. A. Doyle (2009) state:

    "It is unlikely that this 'ancestral flower' was the 'first flower' in a morphological sense, which may have originated much earlier on the angiosperm stem lineage ..."

    The preceding two quotations are from page 23 of P. K. Endress and J. A. Doyle. (2009), Reconstructing the ancestral angiosperm flower and its initial specializations. American Journal of Botany 96(1): 22-66.

    A solitary carpel of the "living fossil" magnoliid tree, Degeneria vitiensis (Degeneriaceae, Magnoliales), is depicted in the right-hand scanning electron micrograph, ×15.

    The Degeneria reproductive organ was field-fixed in 1986 from a dissected flower collected in the canopy of a tagged and vouchered tree growing in a stand on the slopes of Mount Naitaradamu on Viti Levu Island, Fiji. Students should compare this scanning electron micrograph with the Zogg sample prepared by Peter Endress (page 563, Figure 21, 2015).

    The scanning electron micrograph was prepared by Al Soeldner, Director, Oregon State University Electron Microscopy Laboratory. I thank the National Geographic Society for providing research funding for this study.

    "What do flowers of living basal angiosperms tell us about the early evolution of flowers?" (quoted from page 1095, Endress and J. A. Doyle 2015). Some clues from combined morphological- and molecular phylogenetic analyses are reviewed by these authors, which are distilled in the bulleted list below:

  • floral phyllotaxis was probably both spiral and whorled in ancestral angiosperms (see Figure 3 on page 1096);
  • the ancestral floral bauplan was bisexual (unisexuality in Amborella trichopoda is an apomorphy;
  • early flowers were probably protogynous;
  • both the D + E and J + M backbone cladograms show that the ancestral carpel was ascidiate (see Figure 4 on page 1098);
  • carpel closure in ancient flowering plants was achieved by sealing (see the right-hand SEM, above), but not by post-genital fusion as thought by Cronquist and others;
  • studies of Late Mesozoic fossilized flowers and fruits indicates that the uniovulate condition is plesiomorphic (see also Figure 6 on page 1100);
  • four-nucleate embryo sacs might be ancestral (evidence is equivocal according to Endress and J. A. Doyle (2015).
  • Based on mounting evolutionary-developmental, morphological, and paleobotanical evidence, the floral bauplan is probably considerably more ancient than generally thought by Chanderbali et al. (2016).

    Unequivocal stem group angiosperms remain unknown (D. E. Soltis et al. 2007, Stephen A. Smith et al. 2010) despite the assertion of other workers that "considerable progress" appears in the literature on identifying "the earliest lineages of flowering plants" (page 1581, Rudall et al. 2009).

    "Some authors seem curiously determined to prove that pre-Cretaceous fossils are crown-group angiosperms, but for understanding most aspects of the origin of angiosperms [other than their age], close stem relatives would be far more significant ..."

    The preceding statement is quoted from page 318 of J. A. Doyle (2012), Molecular and fossil evidence on the origin of angiosperms. Annual Review of Earth and Planetary Sciences 40: 301–326.

    Confounding floral morphospace. A permineralized compound cone recovered from a concretion found in a North American Valanginian rock outcrop on Vancouver Island yielded a surprising trove of cupules, ovules, axillary shoots, bracts, and megasporophylls attached to a mostly complete female cone axis (Rothwell and Stockey 2016).

    "FIGURES 10-15 Doylea tetrahedrasperma Stockey and Rothwell. All sections are from concretion P13467. (10) Longitudinal view of bract/axillary fertile shoot complex sectioned in approximately radial view of cone, showing diverging bract tip [b] and one sporophyll-bearing ovule. Note elongated scale tip [st], and recurved lobe of sporophyll [arrow] extending back along ovule side. Numbered lines at base of photo correspond to levels at which figures of same number are sectioned. C top no. 60, ×20 ..." This copyrighted figure was reproduced with written permission from the Editorial Office of the American Journal of Botany.

    Did ancient seed plants bearing reproductive short- [spur-] shoots display an ancestral, developmentally-plastic, floral bauplan? Based on Figure 10 (see the left-hand image, Rothwell and Stockey 2016), species of Mesozoic Doyleales did not.

    Are certain homologies of reproductive organs of Caytonia proposed by J. A Doyle (pages 380-385, 1978), congruent with classical studies of Arber and Parkin, Leppik, Stebbins, and Takhtajan? No, when biochemical and evolutionary-developmental (evo-devo) models of cone and floral organization posited by Baum and Hileman (2006), Theißen and Melzer (2007), and Melzer et al. (2010), are considered.

    "... Many authors have noted the similarity of petriellalean cupules to those of the Caytoniales, a group of gymnosperms that continues to figure prominently in theories about the mysterious origin of flowering plants ... Recent hypotheses propose that the earliest angiosperms may have been small, woody shrubs that colonized disturbed sites in the damp understory of humid forests ... The reconstructed physiology and ecology of the Petriellales matches this life form to such detail that we suggest these unusual gymnosperms may represent convergent ecological analogues of early flowering plants" (page 1074, Discussion, Ecology and Paleoenvironment, Bomfleur et al. 2014).

    Taking into account the morphology of reproductive short shoots of Winteraceae (i.e. the supposed source of shed Afropollis), Bomfleur and coauthors (op. cit.) should understand that petriellalean cupules are incompatible with tool kit models of floral development from spur shoot apical meristems.

    "... We anticipate that the evident question-whether beyond the mere ecological similarity there may be phylogenetic relationships linking Petriellales with angiosperms-will be answered once more detailed information about their reproductive biology becomes available" (page 1074, Discussion, Ecology and Paleoenvironment, Bomfleur et al. 2014).

    Caytoniales, Corystospermales, Doyleales, and Petriellales probably had nothing to do with the evolution of stem-group flowering plants or the origin of angiosperms. Consequently, Figure 6 on page 827 of J. A. Doyle (2008), former iterations of this seed plant phylogeny, and some hypotheses billed as "theories" (Frohlich 2002), are probably incorrect.

    Based on this fragmentary body of sometimes credible data, a 160 million year old ghost lineage or lineages of flowering plants is possible, thus paralleling the vexing problems in deciphering early Mesozoic insect and dinosaurian lineages, including challenges to the validity of the so-called Cretaceous Terrestrial Revolution (G. T. Lloyd et al. 2008). More paleontological data are critically needed in line with suggestions by E. L. Taylor and T. N. Taylor (2009).

    The remaining sections of this third and last essay review high points of the vast literature that covers the Mesozoic fossil history of crown group flowering plants. There is brief mention of extant plant biology and phylogenetics to accompany these paleobotanical snapshots. Some important work is not cited. Students should use book chapter bibliographies or Google Scholar to research other titles not listed below. Accomplished albums on fossil plants, floral evolution, and insect biology are published in important reference book chapters or books by Grimaldi and Engel (2005), T. N. Taylor et al. (2009), J. A. Doyle and Endress, (2011), Friis et al. (2011), and Gomez et al. (2012).

    Angiosperm classification. It is important to review the phylogenetic position and naming of modern flowering plant groups within a general evolutionary framework for purposes of later comparison and discussion.

    Professor Tod Stuessy (2009) presents cogent arguments discussing the pros and cons of a universal phylocode.

    Classification levels of order and genus are used in the tabulations below because the number of genera in extant floras is the most commonly used biogeographically significant measure of biodiversity. Principal references on angiosperm classification and floristics are Engler (1964), Thorne (1968), Dahlgren (1980), Cronquist (1981), Dahlgren and Clifford (1982), Dahlgren et al. (1985), Thorne (1992), Takhtajan (1997), Thorne and Reveal (2007), Angiosperm Phylogeny Group (2009), Chase and Reveal (2009), Endress and J. A. Doyle (2009), and Takhtajan (2009).

    Cladistics is a scientific tool with mathematical and theoretical limitations (Graur and Martin 2004) that should not be a final determinant of classification (Stuessy 2009). It (cladistics) is not a "science" in my opinion, despite Cracraft's statement (page 348, 2005).

    "The only way to identify fossil stem relatives of angiosperms is by consideration of their morphological characters, preferably analyzed with cladistic methods."

    The preceding statement is quoted from page 819 of J. A. Doyle (2008), Integrating molecular phylogenetic and paleobotanical evidence on the origin of the flower, International Journal of Plant Sciences 169(7): 816-843.

    The graphic below is redrawn from APG III (page 108, Figure 1, 2009). The APG III phylogenetic tree shows relationships of some families and orders of angiosperms supported by jackknife and bootstrap frequencies over 50% or Bayesian posterior probabilities > 0.95 (not all flowering plant families are included), based on molecular data (APG III 2009).

    Douglas Soltis and co-workers offer one of several updates of the ongoing research effort to compute the angiosperm tree of life from molecular data (D. E. Soltis et al. 2010). A companion to APG III is published as an updated molecular based phylogeny of flowering plants by D. E. Soltis et al. (2011), which incorporated studies of 17 genes and 640 species.

    Molecular phylogenetic studies of extant flowering plants now incorporate the nuclear gene Xdh (Morton 2011). The Angiosperm Phylogeny Group has now published version four (APG IV 2016).

    The color of typescript in the remainder of figures on this web page allows visual cross reference to subclasses of flowering plants (Cronquist 1981) where a discussion of characters is available. Monocots are in various shades of green or orange (Alismatidae are denoted by blue-green type, Arecidae with yellow type, Zingiberidae are shown in gold letters, Commelinidae have green letters, and Liliidae are depicted in lime green type).

    Magnoliidae are shown with indigo brown type. Hamamelidae are depicted with magenta letters. Dilleniidae appear on the dendrogram labels in royal blue. The Caryophyllidae are depicted in purple type. Rosidae are colored red and Asteridae appear in black type.

    Fossil history. Fossilized pollen casings known as palynomorphs are known from middle Triassic sediments recovered from deep well bore holes drilled off the island of Spitzbergen (Hochuli and Feist-Burkhardt 2004). These palynomorphs may represent the first Mesozoic records of stem group angiosperms, but whole plant fossils are lacking (Friis et al. 2005).

    Yet another important study of pollen samples recovered from isolated sedimentary layers in [at least one] continuous stratigraphic sequence in two deep well cores, reports monosulcate, columellate palynomorphs, and Afropollis, from the Middle Triassic (Anisian) about 240 MYA (Hochuli and Feist-Burkhardt 2013).

    The right-hand image is "PLATE I ¦ Scale bar[s] 10µm. (1), Pollen Type 1, specimen A, LM image (high focus)" (Hochuli and Feist-Burkhardt 2013): micrograph is reproduced by permission from Professor Peter A. Hochuli, Palaeontological Institute and Museum, University of Zürich, Zürich, Switzerland.

    "We have examined herein different methodological approaches (i.e. fossil-based, molecular, phylogenetic and paleobiogeographic studies) and current viewpoints about the explosive Cretaceous diversification of angiosperms. After integrating evidence as a whole with our results, the resulting scenario suggests that there is nothing particularly mysterious about the diversification of angiosperms during Cretaceous times or how it is reflected in the fossil record. The clade probably first appeared during Triassic times, possibly as a result of the re-setting of plant evolutionary history following the devastating global extinction event of the Permian–Triassic boundary ..." (4. Conclusions, Cascales-Miñana et al. 2016).

    Sanmiguelia. Of all the enigmatic seed plants of the early Mesozoic Era, Sanmiguelia lewisii has attracted the most attention by students of angiosperm paleobiology (S. Ash 1976, Burger 1981, Cornet 1986, 1989, S. Ash and Hasiotis 2013). This rather common Triassic fossil of southwestern North America is remarkably similar to the Paleozoic Vojnovskyales (page 779, Crane 1985).

    Crane (1985) suggested that some populations of late Paleozoic Vojnovskyales might have survived the end-Permian extinction reappearing in the Triassic rock record as the seed plant Sanmiguelia. Does this overlooked and thoughtful comparison merit further exploration? Yes.

    "The male structures [of Sanmiguelia] appear to be strobili with sessile pairs of pollen sacs, more reminiscent of ginkgophytes than angiosperms, and the smooth monosulcate pollen has no angiosperm features" (page 319, J. A. Doyle 2012).

    Was Sanmiguelia lewisii a stem group angiosperm? Possibly, but this determination must be validated by way of paleobotanical evidence yet to be mined from the rocks. The problem is also semantic as expressed in conflicting opinions on the definition of angiosperms, flowers, and from opposing ideas on supposed character homologies with organs of Paleozoic seed plants.

    Sanmiguelia lewisii was an innovative Triassic plant having palm-like leaves (Brown 1956, Ash 1976) with flowers and angiosperm-like reproductive modules not unlike the monocotyledonous angiosperm Veratrum (Cornet 1986, 1989). Detailed studies of the reproductive morphology of Sanmiguelia have been published (Cornet 1989). Additional permineralized fossil material of Sanmiguelia is probably needed to better understand the anatomy of reproduction and whole plant morphology.

    Ovuliferous inflorescences (first described as Axelrodia burgeri), polleniferous inflorescences (named Synangispadixis tidwellii), flowers with ovuliferous units and polleniferous units, megasporophylls as carpels, synangia as anthers, bracts, and bitegmic ovules were described and discussed by Cornet (1986, 1989).

    Uncanny similarities of early Mesozoic seed plant Sanmiguelia lewisii (Cornet 1986, 1989) with Paleozoic Vojnovskyales pointed out by Crane (1985) require confirmation by cladistic analysis of reproductive and vegetative characters gleaned from detailed anatomical studies of more fossilized remains to be collected. This is an unstudied chronocline with potentially profound implications toward the idea of paraphyletic transitions in diverging seed plants at the base of the angiosperm stem(s) that straddle the PTr boundary.

    Pannaulika and other enigmatic forms. Triassic angiosperm fossils of detached "dicot-like" leaves described as Pannaulika triassica are known (Cornet 1993). However, the Pannaulika leaf find requires discovery of attached sexual organs and stems. Paleobiologists should not forget that lamid palynomorphs referable to Acanthaceae are known from sediments Triassic in age (Tripp and McDade 2014). Further, Hochuli and Feist-Burkhardt data (2004, 2013) are unequivocal.

    Friis et al. (2005) underscore the importance of studying poorly known Mesozoic gymnosperms in order to elucidate the roots of the angiosperm stem group. I concur. Stem group flowering plants are almost completely unknown except for tantalizing clues to their existence from fossil finds of angiosperm palynomorphs, which were recovered from deeply buried Middle Triassic sediments and later discussed by Hochuli and Feist-Burkhardt (2013).

    Comprehensive accounts of the past literature on Mesozoic angiosperms are published by Dilcher (1979), Crane et al. (1986), Crane and Herendeen (1996), Crepet et al. (2004), Friis et al. (2006), Friis et al. (2009), and Friis et al. (2011).

    Fossils of several other enigmatic flowering plants have been recovered from Mesozoic rocks but reproductive details and the morphology of whole plants are unclear due to problems with poor preservation and uncertain stratigraphic control (Müller 1981, G. Sun and Dilcher 1997, G. Sun et al. 1998, G. Sun et al. 2001, Friis et al. 2006, Xin Wang et al. 2007, Zhong-Jian Liu and Xin Wang 2015).

    I completely reject the assertion by some workers that angiosperms first appeared in the Cretaceous Period (Feild and Arens 2007). Absence of fossilized remains of flowering plants in the stratigraphic record is not data.

    Table 6 summarizes the stratigraphic distribution and microfossil, megafossil, and mesofossil history of the subclasses of flowering plants according to Cronquist (1981). I did not include numerous reports and descriptions of Mesozoic leaf morphotype genera (Dilcher and Basson 1990, Upchurch and Dilcher 1990, among others) to avoid guesswork on their taxonomic placement without benefit of reproductive structures.

    Detailed discussion is published in Chapter 22 of the most recent comprehensive treatise on fossil angiosperms (T. N. Taylor et al. 2009). The data contained in T. N. Taylor et al. (2009) are more complete and detailed than my brief summary (Tables 6-13).

    "Angiosperm phylogeny is riddled with examples of convergent morphologies ... Any classification based on a single organ has a greater potential for error than one based on a variety of organs ... Although one solution to this problem would be to restrict the systematic analysis of angiosperm megafossils to taxa known from both reproductive and vegetative organs, this approach would greatly restrict information about the flora as a whole, given the dominance of isolated vegetative organs in the megafossil record."

    The above statement is from page 3 of Upchurch and Dilcher (1990), Cenomanian Angiosperm Leaf Megafossils, Dakota Formation, Rose Creek Locality, Jefferson County, Southeastern Nebraska, U.S. Geological Survey Bulletin 1915.

    Integers in Table 6 represent the total number of taxonomic orders and genera (in parentheses) for each of Cronquist's subclasses of flowering plants. Separate columns are devoted to extant and extinct taxa. The number of extant genera (in parentheses) in the table below was compiled from Cronquist's family descriptions (1981). Certain fossil species reported in the scientific literature are not assignable to any extant angiosperm subclass. The Archaemagnoliidae is lumped with the Magnoliidae.


    Table 6. Mesozoic Fossil History of Subclasses, Orders, and Genera of Flowering Plants According to Cronquist (1981).

    Taxonomic Subclass

    Extant Orders (Genera)

    Mesozoic Orders (Genera)

    Malm - Jurassic

    Neocomian - Cretaceous

    Gallic - Cretaceous

    Senonian - Cretaceous

    Not Assignable to a Known Subclass

    Not Applicable

    ?(7)

    ?

    ?(2)

    ?(4)

    ?(4)

    Alismatidae

    4(60)

    2(4)

    0

    1(2)

    1(2)

    ?

    Arecidae

    4(330)

    3(11)

    0

    1(1)

    1(1)

    3(5)

    Asteridae

    11(3584)

    ?(2)

    0

    0

    0

    2(2)

    Caryophyllidae

    3(397)

    1(1)

    0

    0

    0

    1(1)

    Commelinidae

    7(703)

    1(1)

    0

    0

    0

    1(1)

    Dilleniidae

    13(1452)

    5(11)

    0

    0

    3(4)

    5(7)

    Hamamelidae

    11(148)

    3(18)

    0

    0

    3(13)

    5(24)

    Liliidae

    2(1463)

    1(1)

    0

    0

    1(1)

    1(1)

    Magnoliidae

    8(482)

    6(45)

    0

    5(6)

    12(34)

    2(5)

    Rosidae

    18(3185)

    10(23)

    0

    0

    5(12)

    9(19)

    Zingiberidae

    2(134)

    1(2)

    0

    0

    0

    1(1)


    There is a significant increase in the number of orders and genera of fossil flowering plants by the Aptian Age of the Gallic Epoch of the Cretaceous Period, based on data in Table 6. When the compression floras of leaves are added, a late Cretaceous radiation of angiosperms is remarkable (Friis et al. 2006).

    The Cretaceous to Neogene "Assemblage 4: Angiosperms and the Later Phase of the Modern Insect Fauna" (page 254, Labandeira 2000) is concordant with the view that, "... no other reason than flowering plants and holometabolous insects essentially have monopolized almost all of the terrestrial (and many freshwater) habitats during this interval ..."


    Crown Group Flowering Plants:

    This chapter reviews the scientific literature on the basic biology of extant basal angiosperms of the crown group, and summarizes the fossil record of magnoliids, monocots, eudicots, and core eudicots (rosids and asterids).

    Insights into the rapid radiation of crown group flowering plants from the angiophyte stem group based on contrasting molecular phylogenetic research perspectives are available in numerous reviews (J. A. Doyle and Donoghue 1993, Magallón and Castillo 2009, Stephen A. Smith et al. 2010, Burleigh et al. 2011, D. E. Soltis et al. 2011), among others.

    Pictured to the left is a flower of Protea compacta (Proteaceae, Proteales, Proteanae) photographed by the author.

    Molecular phylogenetic studies suggest that differentiation of flowering plants into a Mesozoic stem and crown group is feasible (Hilu et al. 2003, Davies et al. 2004, Leebens-Mack et al. 2005, R. K. Jansen et al. 2007, Stephen A. Smith et al. 2010, Burleigh et al. 2011, D. E. Soltis et al. 2011), among others.

    The Cretaceous Yixian Formation of Asia yields potentially interesting fossilized inflorescences, flowers, seed, and pollen of crown group angiosperms including Asiatifolium, Jixia, Leefructus, Shenkuoa, and Xingxueina (G. Sun et al. 2001, G. Sun et al. 2011). Many of these fossil genera probably belong in the lower eudicot or magnoliid clades.

    Research findings on the Cretaceous Yixian Formation and other strata from northeastern Asia are reviewed by Ge Sun et al. (2008) and G. Sun et al. (2011).

    Archaefructus liaoningensis (Magnoliophyta, Magnoliopsida, Archaemagnoliidae) was described by G. Sun and Dilcher in 1997, and discussed within the context of a Jurassic aquatic origin of flowering plants (G. Sun et al. 1998). Radioisotope decay data suggest that the Yixian Formation is much younger than originally believed by Ge Sun and colleagues (see Friis et al. 2006).

    Phylogenetic placement of Archaefructus as a stem group flowering plant is problematic (Friis et al. 2003, J. A. Doyle 2008). Several workers suggest that the angiosperm fossils from the Cretaceous Yixian Formation are better placed with the crown group of eudicot angiosperms.

    Hyrcantha decussata (Sinocarpus decussatus, Leng and Friis 2006) is one of the controversial angiosperm-like fossils recovered from northeastern Asian Cretaceous sediments (Dilcher et al. 2007). It is increasingly unlikely that any of the aforementioned taxa belong in the angiosperm stem group.

    Fossilized flowers are also known from exposed Cretaceous sediments of Antarctica (Eklund 2003), Asia (G. Sun et al. 1998, Poinar and Chambers 2005), North America (Crane and Herendeen 1996), South America (Endressinia brasiliana, Mohr and Bernardes-de-Oliveira 2004), and elsewhere (Friis et al. 2006), among others.

    Another interesting but incomplete Cretaceous North American angiosperm fossil is Archaeanthus linnenbergerii (Dilcher and Crane 1985). The morphology of pollen-bearing organs and stem anatomy of Archaeanthus is unknown, therefore critical comparison with Afropollis pollen and fossil wood of Cretaceous Winteraceae from Antarctica (Poole and Francis 2000) is impossible.

    "It seems the perpetuation of the 'abominable mystery' is due more to a disagreement over the cladistic position of various fossil taxa in relationship to the angiosperm crown group, than the lack of data."

    The preceding quotation is from page 127 of M. S. Zavada (2007), The identification of fossil angiosperm pollen and its bearing on the time and place of the origin of angiosperms, Plant Systematics and Evolution 263: 117-134.

    The APG III classification system (Chase and Reveal 2009) will require revision to accommodate results of ongoing molecular phylogenetic research (D. E. Soltis et al. 2011). This task is now complete with the publication of APG IV in 2016. Some workers in the past (D. E. Soltis and P. S. Soltis 2003) suggested abandoning the angiosperm subclass system enthusiastically followed by Arthur Cronquist (1981) and others, but this idea might be too inflexible, in my opinion.

    A temporary fix to preserve Arthur Cronquist's accomplished work is to adopt the classification level of superorder as championed by Dahlgren and Clifford (1982) and Dahlgren et al. (1985) for monocots, and proposed by Chase and Reveal (2009) for flowering plants as a whole. Some Cretaceous angiosperm and mesoangiosperm fossils do not fit in Chase and Reveal's superorders, therefore an informal approach is warranted here.

    Tables 7-13 are organized along the lines adopted in T. N. Taylor et al. (2009) with consideration of concepts introduced by Chase and Reveal (2009). These tables are updated to highlight some of the more significant paleobotanical finds of the Second Millennium, which are by no means a complete review of the literature on Mesozoic angiosperm fossils.

    Cretaceous explosive radiation of angiosperms. Rapid radiation of flowering plants during the Albian Age of the early Cretaceous Period is demonstrable based on paleontologic evidence gathered to date (Friis et al. 2006, T. N. Taylor et al. 2009, Friis et al. 2010), molecular evidence from duplication and neofunctionalization of MIKC-type MADS-box genes (Irish 2006), and phylogenetic analyses (D. E. Soltis et al. 2008, Endress and J. A. Doyle 2009).

    McElwain et al. (2005) suggested that the Cretaceous diversification of flowering plants was possibly attributable to decline in atmospheric carbon dioxide levels instead of developing aridity. Rapid radiation of angiosperms might have been "controlled by ecological limits" (abstract, J. C. Vamosi and S. M. Vamosi 2010), or diversification was affected by escalation (Vermeij 2011).

    Wildfire regimes were probably responsible for the rapid spread of the group in Cretaceous times (Belcher 2010).

    Boyce and Lee (2010) suggested that the rise of dominance of angiosperms played a critical role in tropical rainforest biodiversity and expansion from an ecophysiological research perspective.

    Clues to angiosperm diversification may be gleaned from studies of xylem heterochrony (Carlquist 2009).

    Was the Big Bang of angiosperm evolution during the Aptian Age (Gallic Epoch) attributable to the effects of the end-Barremian Age (Neocomian Epoch) biogeochemical perturbation (BaCCE) on coevolving angiosperm hosts and insect antagonists?

    The oldest fossil eudicot, Leefructus, is from Lower Cretaceous units of the Yixian Formation radiometrically dated within the interval 123-124 MYA, which is the Barremian Age (G. Sun et al. 2011).

    Mounting geophysical evidence points toward extensive episodes of Cretaceous (Aptian) volcanism in the southwest Pacific Basin near the undersea Ontong Java Plateau (Tejada et al. 2009). Methane clathrates released from undersea beds could explain significant spikes in atmospheric methane and carbon dioxide, triggering the BaCCE and later carbon cycle anomalies of the Cretaceous Period.

    Heimhofer et al. (2005) suggest that the BaCCE might have accelerated the diversification of early magnoliid flowering plants and possibly monocots. Phylogenetic analysis supports the idea that an explosive radiation of the order Malpighiales occurred during the Aptian Age of the Gallic Epoch, a few million years after the BaCCE (Davis et al. 2005, Figure 1).

    In 1981, Friis and Skarby reported a remarkable find of abundant indeterminate and tiny angiosperm eudicot flowers from the Late Santonian-early Campanian Age (Senonian Epoch, Late Cretaceous Period). Friis and Skarby (1981), Friis (1985), Crane et al. (1986), Knobloch and Mai (1986), Schönenberger and Friis (2001), Eklund (2003), Kvaček and Eklund (2003), and Friis et al. (2006) are key pieces of the scientific literature on early angiosperm floras and fossils.

    Studies of Cretaceous permineralized woods (V. M. Page 1967) paint a different picture of Maastrichtian forests once thought to be dominated by gymnosperms. A recent study of wood permineralizations sampled from large, fallen in situ logs from southwestern North American Maastrichtian (Senonian) deposits of the Aguja and Javelina Formation suggests that "dicotyledonous" trees were more abundant than conifers. Petrified stumps of Javelinoxylon multiporosum (Malvales, Dilleniidae) were more than a meter in diameter with extrapolated tree axes up to 40 meters tall (Wheeler and Lehman 2000).

    Existence of dilleniid Javelinoxylon trees belonging to derived crown group eudicots as an important floristic element of late Cretaceous stratified tropical forests of southwestern North America (Wheeler and Lehman 2000), and large trees of Paraphyllanthoxylon indigenous to European forests of that time (Oakley and Falcon-Lang 2009), detract from the idea that early flowering plants were paleoherbs of upland habitats.

    A paper by Bond and A. C. Scott (2010) suggests that "novel fire regimes" affected the rapid diversification and evolution of crown group flowering plants.

    Basal angiosperms. The floral biology and evolution of basal angiosperms and magnoliids is reviewed by Peter Endress (2010). An APG update (APG III 2009) includes a "working classification" (pages 123 and 124, Table 1, Chase and Reveal 2009), which I adopted in this essay. The Angiosperm Phylogeny Group has now published its fourth cladogram of crown-group flowering plants (APG IV 2016).

    The water lily above is Nymphaea odorata var. rosea (Nymphaeaceae, Nymphaeales, Nymphaeanae).

    A benchmark phylogenetic study by Y.-L. Qiu (2000) established a group of extant flowering plant families as basal to all other living angiosperms. Phylogenetic inference from genomic data including more than 18,000 gene trees by Burleigh et al. (abstract, 2011) supports placement of magnoliids as "sister to a eudicot + monocot clade."

    Chase and Reveal (2009) recognize four superorders of basal angiosperms and magnoliids: Amborellanae, Austrobaileyanae, Magnolianae, Nymphaeanae. Chloranthales are unplaced (Chase and Reveal 2009).

    The classification proposed by Chase and Reveal (2009) for angiosperms is accompanied by a scheme for extant gymnosperms, which is published by Christenhusz et al. (2011).

    Certain ANITA grade basal flowering plants first appear in the fossil record of the Cretaceous Period (Friis et al. 2000, Friis et al. 2001, Krassilov and Golovneva 2004, Takahashi et al. 2007, von Balthazar et al. 2008). The fossil history of basal angiosperms is reviewed by Friis et al. in three reviews (2006, 2009, 2010).

    Douglas E. Soltis et al. (2005) provide a detailed discussion of basal flowering plants which is updated in a recent review (D. E. Soltis et al. 2008). Alexandr Rasnitsyn and Donald Quicke (2002) edit the most complete book on Triassic, Jurassic, and Cretaceous fossil insects available at this time.

    A book on Mesozoic seed plants including crown group basal angiosperms is T. N. Taylor et al. (2009). The extensive discussion, graphics, and tables presented in the four monumental works cited above will not be repeated here; however data are cited when appropriate.

    D. E. Soltis et al. (2005) support the assignment of ANITA grade angiosperms to a basal position in several calibrated, bootstrap supported, molecular-based phylogenies of extant flowering plants. The acronym ANITA is composed of first letters from the taxa Amborella, Nymphaeales, Illiciaceae, Trimeniaceae, and Austrobaileyaceae.

    Since 2005 phylogenetic analyses of extant basal flowering plants point to the Amborellaceae, Nymphaeales, and Austrobaileyales (ANA) as sister groups to all other basal magnoliids, monocots, eudicots, core eudicots, rosids, and asterids (Leebens-Mack et al. 2005, Y.-L. Qiu et al. 2006, Frohlich and Chase 2007, D. E. Soltis et al. 2008, Magallón and Castillo 2009). Reevaluation of gymnosperm molecular sequences when subjected to phylogenetic analysis (Y.-L. Qiu et al. 2001) support the basal position of ANITA grade angiosperms with respect to magnoliids, monocots, and eudicots.

    This line of research continues (Zhenxiang Xi et al. 2014). Related papers by Drew et al. (2014), D. W. Taylor and Gee (2014), Goremykin et al. (2015), Simmons and Gatesy (2015), and M. L. Taylor et al. (2015) should be read, among others. Further, the elaborate analyses published by Goremykin et al. (2015), yield results concordant with Zhenxiang Xi et al. (2014).

    "... regardless of whether Amborella alone is the sister to all other extant angiosperms or whether Amborella + Nymphaeales form a clade, one cannot infer the habit or habitat of the first angiosperms based on the morphology of extant taxa" (page 379, Discussion, Drew et al. 2014).

    The genome-scale molecular phylogenetic analyses by Zhenxiang Xi et al. (2014) are the first to resolve an Amborella + Nuphar phylogenetic couplet as sister to all other extant angiosperms when coalescent techniques are employed in computation, simulations, and tree-thinking.

    "... Our results lend further empirical support for analyzing genome-scale data to resolve deep phylogenetic relationships using coalescent methods, and provide the most convincing evidence to date that Amborella plus Nymphaeales together represent the earliest diverging lineage of extant angiosperms" (page 929, Results and Discussion, Accommodating Elevated Rates of Substitution in Coalescent versus Concatenation Analyses, Xi et al. 2014).

    A review and phylogenetic analysis incorporates early Cretaceous fossil data with input from extant basal angiosperms and magnoliids (J. A. Doyle and Endress 2010).

    Basal flowering plants sensu Cronquist (1981) belong to Amborellaceae and Trimeniaceae (Laurales), Austrobaileyaceae (Magnoliales), Hydatellales (monocots), Illiciales, and Nymphaeales.

    Certain other Magnoliales once regarded by Cronquist (1981) as primitive angiosperms (Annonaceae, Degeneriaceae, Lactoridaceae, Magnoliaceae, and Winteraceae) are in a more derived position on phylogenetic trees based on molecular data (Wikström et al. 2001, Davies et al. 2004, Leebens-Mack et al. 2005, Y. L Qiu et al. 2006, D. E. Soltis et al. 2007) than ANITA grade taxa.

    Tremendous progress has been made on understanding the anatomy, basic biology, organelle genetics, developmental genetics, ecology, floral genetics, molecular evolution, morphology, natural history, and phylogenetic systematics of ANITA grade basal angiosperms (Parkinson et al. 1999, J. A. Doyle and Endress 2000, Endress and Igersheim 2000, Floyd and Friedman 2000, S. W. Graham and Olmstead 2000, Mathews and Donoghue 2000, Y. L Qiu et al. 2000, P. S. Soltis et al. 2000, Thien et al. 2000, Endress and J. A. Doyle 2015).

    Work on ANITA grade basal angiosperms is published by Endress (2001), Furness and Rudall (2001), Friedman (2001), Yamada et al. (2001), Borsch et al. (2003), Feild et al. (2003), Ronse De Craene et al. (2003), E. L. Schneider et al. (2003), Zanis et al. (2003), Aoki et al. (2004), Endress (2004), Stefanovič et al. (2004), Carpenter (2005, 2006), Endress and J. A. Doyle (2007), Feild and Arens (2007), Rudall et al. (2008), Endress (2008), Sage et al. (2009), P. S. Soltis et al. (2009), Thien et al. (2009), Zuccolo et al. (2011), and Lu Lu et al. 2015, among others.

    Despite elucidation of MIKC-type MADS-box gene function in several groups of flowering plants (Irish 2006), the importance of MIKC-type MADS-box A function in basal angiosperms is unclear (D. E. Soltis et al. 2007). Molecular phylogenetic work has been published by S. Kim et al. (2005), Leebens-Mack et al. (2005), Podoplelova and Ryzhakov (2005), Y. L Qiu et al. (2005), Zahn et al. (2005), P. S. Soltis et al. (2006), Moore et al. (2007), D. E. Soltis et al. (2007), and P. S. Soltis et al. (2009).

    Zahn et al. (2005) report MIKC-type MADS-box E gene homologs of SEP from basal angiosperms. The molecular phylogenetic studies by Zahn et al. (page 2220, 2005), "strongly supports the hypothesis that the SEP subfamily has been present in the angiosperms since before the diversification of the extant basal-most angiosperms Amborella and the Nymphaeales."

    Transcription factors (TFs) and phylogenetic analyses of the genes encoding them are the subject of focused studies of non-model basal flowering plants and magnoliids, which are published in two key papers (Howarth and Donoghue 2006, Horn et al. 2014).

    Pollination ecology of primitive flowering plants has the subject of much field research and debate over the past 20 years, even before the term basal was widely used by plant systematists. Certain beetles (Coleoptera) are considered pollinators of basal angiosperms but the list also includes several groups of flies (Diptera), moths (Lepidoptera), and wasp-like bees (Hymenoptera). A review of some of these studies (Bernhardt et al. 2003) adds considerable controversy to the role of stigmatic secretions as pollinator attractants, and calls into question character polarity of wet type stigmas determined by Endress and Igersheim (2000).

    Amborellanae. Volume 342, Number 6165 of Science publishes three significant papers on paleopolyploidy and the genome ecology of Amborella trichopoda, which is a specialized, root-sprouting understory endemic shrub of the high island of New Caledonia (Nouvelle Caledonie), southwest Pacific Ocean.

    "The Amborella genome is a pivotal reference for understanding genome and gene family evolution throughout angiosperm history. Genome structure and phylogenomic analyses indicate that the ancestral angiosperm was a polyploid with a large constellation of both novel and ancient genes that survived to play key roles in angiosperm biology" (Structured Abstract Discussion, Amborella Genome Project 2013).

    Earlier installments of this ongoing work were published in Genome Biology by D. E. Soltis et al. (2008) and Zuccolo et al. (2011).

    Detailed next-generation sequencing studies by Srikar Chamala et al. (2013) report use of fluorescence probes to disentangle and decipher the large genome of Amborella trichopoda (Amborellaceae), a nonmodel basal angiosperm.

    "Transposable elements in Amborella are ancient and highly divergent, with no recent transposon radiations" (Abstract, Amborella Genome Project 2013).

    Earlier research papers that focus on Amborellanae include I. W. Bailey and Swamy (1948), Tobe et al. (2000), Endress and Igersheim (2000), Feild et al. (2001), Hesse (2001), Yamada et al. (2001), Goremykin et al. (2003), Posluszny and Tomlinson (2003), Thien et al. (2003), Bergthorsson et al. (2004), Buzgo et al. (2004), D. E. Soltis and P. S. Soltis (2004), Yamada et al. (2004), Duarte et al. (2008), D. E. Soltis et al. (2008), Friedman and Ryerson (2009), and Williams (2009), among others.

    Basalmost position (or near basalmost) of the angiosperm crown group species Amborella trichopoda in some molecular based phylogenies is challenged by Goremykin et al. (2003). This seemingly anomalous finding is explained and eloquently refuted in two papers (D. E. Soltis and P. S. Soltis 2004 and Stefanovič et al. 2004).

    The Amborella genome does not show evidence of extensive WGDs (D. E. Soltis et al. 2008, Amborella Genome Project 2013), it is troubling that YABBY2 genes in the species are expressed on adaxial leaf surfaces (Yamada et al. 2004).

    From the research perspectives of molecular coevolution, paedomorphic heterochrony, and reproductive biology, the most curious finding uncovered thus far by the Amborella Genome Project is "that the density of long terminal repeat retrotransposons is negatively correlated with that of protein coding genes" (abstract, Zuccolo et al. 2011).

    Further, it is probably important for these workers to sequence the genomes of other basal flowering plants including water lilies and magnoliids for syntenic comparison with Amborella and avocado.

    Nymphaeanae. Clément Coiffard and co-workers report a definitive fossil find of crown group Nymphaeales from the early Cretaceous South American Crato Formation. This study together with an earlier report of water lily fossils from the Crato Lake Paleoflora (Mohr et al. 2008) adds more intrigue on the paleobotany of basal flowering plants.

    The left-hand image is Figure 1B on page 144 of Coiffard et al. (2013), "Jaguariba wiersemana gen. nov. et sp. nov.: morphology. B, complete plant, paratype (1999/615)." The scale bar at the lower right of the image is 1 cm.

    Figure 1B is reproduced by permission from the International Association for Plant Taxonomy, Bratislava, Slovak Republic through Professor Joachim W. Kadereit, Editor-in-chief of Taxon, which is the "international journal of taxonomy, phylogeny and evolution," copyright ©2013.

    Nymphaeales have been studied by numerous students of ANITA grade angiosperms including Yamada et al. (2003), Dorn et al. (2004), Les et al. (2004), Vogel and Hadacek (2004), Yoo et al. (2005), Grob et al. (2006), Borsch et al. (2007), Löhne et al. (2007), Borsch et al. (2008), Löhne et al. (2008), Nixon (2008), D. W. Taylor (2008), M. L. Taylor et al. (2008), P. A. Volkova and Shipunov (2008), and Zhou and Fu (2008), among others.

    Published work on the Nymphaeales is authored by Carlquist et al. (2009), Carlquist and E. L. Schneider (2009), Friis et al. (2009), Hu et al. (2009), J.-K. Li and Huang (2009), Rudall et al. (2009), E. L. Schneider et al. (2009), M. L. Taylor and Williams (2009), Williams et al. (2010), Yin et al. (2010, D. W. Taylor and Gee 2014, Povilus et al. (2015), and M. L. Taylor et al. 2015).

    Contributions to the Nymphaeales Symposium are published in Volume 57, Number 4 of the November 2008 issue of the journal Taxon (Borsch and P. S. Soltis 2008). The perianth biology of Nymphaeales figures prominently in a "Mosaic Theory for the Evolution of the Dimorphic Perianth" (Warner et al. 2009).

    Based on the potential importance of water lilies and their close relatives in understanding the evolution of angiosperms, Cabomba (Nymphaeanae, Nymphaeales, Nymphaeaceae) emerges as a key experimental model basal flowering plant (Vialette-Guiraud et al. 2011), together with Amborella and Persea.

    Hydatellaceae regarded by Cronquist (1981) as advanced commelinid monocots now occupy a basal position together with extant ANITA grade dicots (Rudall et al. 2007, Saarela et al. 2007, Friedman 2008, Remizowa et al. 2008, Rudall et al. 2008, Rudall et al. 2009, Sokoloff et al. 2009, Sokoloff et al. 2010, M. L. Taylor et al. 2010, Prychid et al. 2011). According to one review, Hydatellaceae do not shed new light on the enigmatic origins of floral morphology (P. S. Soltis et al. 2009).

    Austrobaileyanae. Hao et al. (2000), Carlquist and Schneider (2002), Friedman et al. (2003), Williams and Friedman (2004), Denk and Oh (2005), Lyew et al. (2007), Morris et al. (2007), and Ye Sun et al. (2010) have published results of detailed studies of the Schisandraceae (including Illiciaceae). Work on the paleobotany and pollination biology of Trimeniaceae appears in research published by Bernhardt et al. (2003) and T. Yamada et al. (2008), among others.

    A paleophysiologic approach was used to generate data suggesting that leaves assignable to Lower Cretaceous Austrobaileyales possessed "low gas exchange capacities" (title, Feild et al. 2011). This approach should be applied to older leaf permineralizations and reconciled with findings published by Kevin Boyce, Andy Knoll, and others.

    Finally, I. W. Bailey and Swamy (1949), Endress (1980), Endress (1983), Yamada et al. (2003), Williams and Kennard (2006), and Tobe et al. (2007) report key findings on anatomy, developmental morphology, genetics, and reproductive biology of certain Austrobaileyales.

    Magnolianae. Magnoliids as currently understood consist of four orders: Canellales, Laurales, Magnoliales, and Piperales. Chloranthales are unplaced by Chase and Reveal (2009).

    On the right is a picture of a flower of Degeneria roseiflora (Degeneriaceae, Magnoliales, Magnolianae), and several fragrant flower buds at different stages of maturity. Two of the largest flower buds shown on this kodachrome opened one by one on the next two successive nights, releasing a rose-like fragrance (photographed by the author). Degeneriaceae are related to Winteraceae and Magnoliaceae (A. C. Smith 1981, J. M. Miller 1988, A. C. Smith 1991).

    Molecular phylogenies of the group have been proposed by Azuma (2001), Sauquet et al. (2003), Massoni et al. (2014), and Massoni et al. (2015), among others.

    Additional studies on plastid genes have been published by Y. L. Qiu et al. (1993) and Cai et al. (2006), among others.

    Some of the biogeographically and morphologically interesting species and families of magnoliids have been incompletely studied using modern molecular approaches, or not researched at all. More molecular phylogenetic work is needed to clarify relationships of Degeneriaceae and Winteraceae, both with species indigenous to the high islands of the southwest Pacific on geologic rock formations and fossil island arcs (arcs insulaires fossiles) equal in age to New Caledonia (Nouvelle Calédonie) where Amborella trichopoda occurs.

    Complex insect pollinator-plant interactions evidently were in place in Nymphaeaceae during Cretaceous time (Gandolfo et al. 2004). Yet, only a few genera are known from the early Cretaceous Yixian Formation of Asia and at Crato Lake in Europe, consisting of fossilized, detached plant parts and flowers, and the fossil remains of other plants classifiable in a couple orders and families (Friis et al. 1997, G. Sun and Dilcher 1997, G. Sun et al. 2001, Mohr et al. 2013).

    The anatomy, biogeography, ecophysiology, evolutionary history, molecular systematics, phylogenetic relationships, pollination ecology, reproductive biology, and taxonomy of certain magnoliid basal angiosperms is reviewed by I. W. Bailey and A. C. Smith (1942), I. W. Bailey and Swamy (1951), Canright (1952), Endress (1984), Friis et al. (1986), Bernhardt and Thien (1987), Carlquist (1987), Endress and Hufford (1989), J. M. Miller (1989), Pellmyr et al. (1990), Loconte and Stevenson (1991), Endress (1994), Crane et al. (1994), Carlquist (1996), Friis et al. (1997), Friis et al. (2000), T. N. Taylor et al. (pages 904-917, Chapter 22, 2009), Saunders (2010), Feild et al. (2011), and APG IV (2016), among others.

    Placement of Ceratophyllales and Chloranthales is problematic, which is the subject of considerable ongoing debate and discussion. Model species in these two groups should become high priority targets for focused evo-devo and genomic studies. I briefly discuss Chloranthales as a magnoliid, sensu APG III (2009), below. Detailed commentary on Ceratophyllales and the origin of angiosperms is included in a discussion of eudicots.

    Canellales. Prevailing thought is to place Winteraceae among Canellales rather than Magnoliales as traditionally viewed. Classical ideas on the evolutionary relationships of Drimys, Tasmannia, and Zygogynum with Magnoliaceae should not be eclipsed by molecular studies, and interpretation of floral organs is still open to debate, in my opinion.

    Molecular-phylogenetic studies of Canellaceae support long-distance, intercontinental dispersal rather than vicariance to explain the biogeography of several genera (S. Müller et al. 2015). At least one genus of Canellales (Canella, Canellaceae) is a subject for study of xylem hydraulics and vessel anatomy (Feild et al. 2011).

    Chloranthales. The Angiosperm Phylogeny Group has removed the Chloranthales from the basal angiosperms and magnoliids and placed them as an isolated and later diverging clade (2016).

    "We place Chloranthales on a polytomy with the magnoliid and eudicots/monocots/Ceratophyllaceae clades ..." (page 5, APG IV 2016).

    Hedyosmums have been the subject of classic debates on the biogeography and evolution of flowering plants (pages 97 and 149, Takhtajan 1969). The genus is also well-known as an example of phylogenetic incongruence from biogeographic, evolutionary, genetic, and taxonomic research perspectives (Qiang Zhang et al. 2015).

    Palynological studies by Friis et al. (2015) posit Canrightiopsis as a link to extinct canrightias and modern Chloranthaceae. Interestingly, fossilized stamens of Canrightiopsis of possess monocolpate pollen referable to Clavatipollenites, but the perianth is missing probably due to taphonomic factors.

    Figure 15 on page 2017 of Friis et al. (2015) depicts a refreshed overview of chloranthalean characters in relation to general flowering plant morphologies without resorting to phylogenetics. The treatise of Canrightiopsis by Friis et al. (2015) contains significant discussion of the evolution of Chloranthales in relation to magnoliids with references to work by J. A. Doyle, Endress, and others.

    Laurales. Several assemblages of rich and diverse Laurales, including Lovellea wintonensis (Dettmann et al. 2009), Eucalyptolaurus depreii (Coiffard et al. 2009), and maulidinias (Drinnan et al. 1990, J-D. Moreau et al. 2016) are known from Cretaceous rocks of Australia and Europe. Occurrence of these derived basal magnoliid angiosperms in sediments of the northern and southern hemisphere before the emergence of New Caledonia from the floor of the Tasman Sea, detract from the idea that Amborella trichopoda is an early divergent, ancestral flowering plant.

    A taxonomic rediagnosis of the late Cretaceous palynomorph Rosannia manika by Srivastava and Braman (2010) recovered from eroding Canadian sediments, has implications on possible relationships with Lactoridaceae, an endemic magnoliid to the Juan Fernandez Islands of the South Pacific Ocean. Perhaps the most exquisitely-preserved lauralean fossil flower known to date is reported from 98 million-year-old amber from Myanmar (Crepet et al. 2016).

    Molecular-phylogenetic studies of magnoliids now extend to the camphor and cinnamon clades of extant Laurales, which are assignable to the genus Cinnamomum (J-F. Huang et al. 2016).

    Paleobotanical work in Maastrichtian Age beds of New Zealand uncovers mesofossils assignable to Laurales and Podocarpales (Cantrill et al. 2011).

    Floral phyllotaxis in early magnoliids was whorled but during the Mesozoic diversification and radiation of the Laurales a transition to spiral phyllotaxis probably occurred (Staedler et al. 2007). The Cenomanian fossil magnoliid Mauldinia exhibited whorled floral phyllotaxis (Drinnan et al. 1990). The marginally preserved fossil blossoms of the magnoliids Araripia, Detrusandra, Jerseyanthus, and Virginianthus exhibit spiral floral phyllotaxis (Staedler et al. 2007).

    Studies on the floral genetics and morphology of avocados, cinnamons, and sassafras (Laurales) are published by Chanderbali et al. (2006), Chanderbali et al. (2008), Chanderbali et al. (2009), P.-C. Liao et al. (2010), and K.-F. Chung et al. (2010), among others.

    Looking at the evo-devo of floral development of certain extant species of Laurales from a genomic research perspective, remarkable progress has been made in unraveling the avocado genome (Chanderbali et al. 2008).

    Magnoliales. Basic research on magnoliids is authored by Allouche et al. (2009), Goodrich and Raguso (2009), Lora et al. (2009), Marquínez et al. (2009), Oelschlägel et al. (2009), Rohwer et al. (2009), Staedler and Endress (2009), Su and Saunders (2009), Tamaki et al. (2009), Oppel and Mack (2010), Z.-H. Wang et al. (2010), X. M. Zhang et al. (2010), L. Zhou et al. (2010), Botermans et al. (2011), and Teichert et al. (2011), among others.

    Focused investigations of magnoliid angiosperms include Doust (2001), Endress (2001), Kimoto and Tobe (2001), Sauquet et al. (2003), Cai et al. (2006), Oginuma and Tobe (2006), Xu and Rudall (2006), Buzgo et al. (2007), Staedler et al. (2007), Wanke et al. (2007), Couvreur et al. (2008, two papers), Gamerro and Barreda (2008), García-González et al. (2008), Kimoto and Tobe (2008), Madrid and Friedman (2008), Nie et al. (2008), Su et al. (2008), Takahashi et al. (2008), Viehofen et al. (2008), Watanabe et al. (2008), Pang and Saunders (2014, 2015), and Massoni et al. (2015), among others.

    Molecular-phylogenetic studies of magnoliids by Hervé Sauquet and others (Massoni et al. 2014) reveal unexpected relationships of Degeneria with Myristicaceae. Much of the past molecular-phylogenetic work suggests a close relationship between Degeneriaceae and Himantandraceae (page 89, Figure 3, Massoni et al. 2014). A 26S rDNA isolate from the only Gen Bank sample of Degeneria available, when subjected to phylogenetic analyses, reveals "surprising" results (page 90, Figure 4, Massoni et al. 2014).

    "... we argue that this result is due to an artifact of attraction between the well-known long stem branch of Myristicaceae [Sauquet et al. 2003] and the unusually long branch of Degeneria for 26S rDNA" (page 91, Discussion, 4.5, 26S rDNA Isolate of Degeneria Leads to Long Branch Attraction, Massoni et al. 2014).

    Other studies of magnoliids include del C. Jiménez-Pérez and Lorea-Hernández (2009), Liao et al. (2010), Surveswaran et al. (2010), Weerasooriya and R. M. K. Saunders (2010), Xu and Ronse de Craene (two papers, 2010), and Endress and Armstrong (2011), among others.

    Floral development in Myristicaceae has been studied by Xu and Ronse de Craene (2010).

    Saunders (2010) reviews floral homeotic transformations and morphology of Annonaceae. The study by Saunders complements work on the evo-devo of floral development by Endress and Armstrong (2011).

    Despite many published field and laboratory studies on the basic biology and evolution of magnoliid basal angiosperms (see above citations), the molecular phylogenetic relationships among the component families and genera are unclear. Possibly critical families such as Annonaceae, Degeneriaceae, Magnoliaceae, and Winteraceae are incompletely studied from this research perspective (P. S. Soltis et al. 2009).

    Incremental progress has been made in deciphering the tulip tree genome (Liang et al. 2007, Liang et al. 2008, Liang et al. 2011) but more work at the genomic level is needed on other magnoliid timber tree species including degenerias and magnolias.

    Piperales. The Piperales, including Chloranthaceae, occupy an evolutionary position between true magnoliids and hamamelids (Crane 1989). Several anatomical, evolutionary developmental, molecular phylogenetic, paleobotanical, and taxonomic studies on members of the Piperales appear in the literature including papers by Carlquist (1987), von Balthazar and Endress (1999), J. A. Doyle et al. (2003), S. Kim et al. (2005), G. S. Li et al. (2005), Arias and Williams (2008), Jaramillo et al. (2008), J. F. Smith et al. (2008), Coe and Bornstein (2009), Horner et al. (2009), Samain et al. (2009), and Polevova (2015), among others.

    Classical ideas on wood paedomorphosis (Carlquist 1989, 1996, 2009, among other papers) including innovative evo-devo of a bifacial cambium as the hallmark of ancient flowering plants are revisited in a later study of woodiness in Piperales by Treuba et al. (2015). Students should not forget that the gigantopteroid seed plant, Delnortea abbottiae, possessed a bifacial cambium expressed in a permineralized petiole (discussed in the previous essay).

    Additional work covering these research perspectives appears in print as original research papers and reviews by Kvaček and Friis (2010), Samain et al. (2010), Antonelli and Sanmartin (2011), and Friis and Pedersen (2011), among others.

    A potentially interesting problem from a coevolutionary perspective is addressed by a paper published by Strutzenberger et al. (2010) having to do with shifting geometrid moth antagonists and Piperales host plant species.

    Fossilized stamens, pollen, and small flowers assignable to Chloranthaceae (Eklund et al. 2004, Friis et al. 2006) have been found in sediments Barremian in Age (late Neocomian Epoch, Early Cretaceous). Extinct Piperaleans including Chloranthaceae are represented in the fossil record as pollen classifiable to certain Asteropollenites, Clavatipollenites hughesii, and Stephanocolpites (Crane 1989), but also includes discovery of Zlatkocarpus from the Cenomanian (Kvaček and Friis 2010).

    Stamens and flowers discovered in several younger rock formations of the Late Cretaceous Period add another layer of evolutionary complexity to magnoliids and basal eudicots, including the Hamamelidae and Trochodendraceae (Crane 1989).

    I cast the available data on the fossil history of magnoliids and certain basal flowering plants into Table 7. Please note that the number in each cell represents the number of species (or genera, as the case may be).

    Unclassified angiosperms. Several fossil genera cannot be classified in any of the known superorders of flowering plants sensu Chase and Reveal (2009). There is little agreement among paleobotanists on how to classify these fossil forms.

    The paleontologic record (in bold type) of these enigmatic fossil flowers and fruits is listed in Table 7 together with basal flowering plants and magnoliids of the angiosperm crown group. Table 7 is obviously incomplete. For example, some of the classic late Mesozoic leaf morphotype assemblages are intentionally left-out. Affinities of several well-known leaf forms are not associated with lauralean reproductive organs (Coiffard et al. 2008).


    Table 7. Mesozoic Stratigraphic Distribution of Basal-, Magnoliid-, and Unclassified Angiosperms.

    Order

    Scientific Name and Publication

    Fossilized Remains

    Malm - Jurassic

    Neocomian - Cretaceous

    Gallic - Cretaceous

    Senonian - Cretaceous

    Nymphaeales?

    taxonomy under study (Friis et al. 2001)

    staminate inflorescences and pollen

    0

    ?

    ?

    0

    Laurales

    undescribed (Eklund and Kvaček 1998, Eklund 2000)

    four unnamed flowers

    0

    0

    0

    4?

    Assignment to Superorder in Doubt

    Afrasita lejalnicoliae (Krassilov et al. 2004)

    infructescences

    0

    0

    1

    0

    Piperales

    Anacostia (Friis et al. 1997)

    pollen and fruits

    0

    1

    1

    0

    Assignment to Superorder in Doubt

    Appomattoxia ancistrophora (Friis et al. 1995)

    fruits

    0

    0

    1

    0

    Nymphaeales

    Aquatifolia fluitans (Hongshan Wang and Dilcher 2006)

    leaves

    0

    0

    1

    0

    Assignment in Doubt

    Araripia florifera (Mohr and Eklund 2003)

    flowers

    0

    0

    1

    0

    Magnoliales

    Archaeanthus linnenbergerii (Dilcher and Crane 1985)

    fruit cluster (flowers, bud scales, and leaves described as form genera)

    0

    0

    1

    0

    Assignment in Doubt

    Archaefructus (Sun et al. 1998, 2001)

    flowers and leafy fruiting axes

    0

    2

    0

    0

    Piperales

    Asteropollis (Friis et al. 2000, Eklund et al. 2004)

    palynomorphs inside stamens, staminate inflorescences and pistillate flowers

    0

    1

    0

    0

    Assignment to Superorder in Doubt

    Baasoxylon parenchymatosum (Wheeler and Lehman 2000)

    wood

    0

    0

    0

    1

    Assignment to Superorder in Doubt

    Beipiaoa (Sun et al. 2001)

    fruits

    0

    3

    0

    0

    Nymphaeales

    Brasenites kansense (H. Wang and Dilcher 2006)

    leaves

    0

    0

    1

    0

    Assignment to Superorder in Doubt

    Callianthus dilae (X. Wang and Zheng 2009)

    flower, fruits and pollen

    0

    1

    0

    0

    Assignment to Superorder in Doubt

    Caloda delevoryana (Dilcher and Kovach 1986)

    inflorescence and fruit

    0

    0

    1

    0

    Piperales

    Canrightia resinifera (Friis and Pedersen 2011)

    pollen and flowers

    0

    1

    0

    0

    Austrobaileyales? Nymphaeales?

    Carpestella lacunata (von Balthazar et al. 2008)

    flower

    0

    0

    1

    0

    Piperales

    Chloranthistemon (Crane et al. 1989, Eklund et al. 1997)

    inflorescences and flowers

    0

    0

    0

    >2

    Piperales

    Clavatipollenites (Friis et al. 2000, Eklund et al. 2004)

    palynomorphs inside stamens, staminate inflorescences and pistillate flowers

    0

    1

    0

    0

    Piperales

    Couperites mauldinensis (Pedersen et al. 1991)

    fruits

    0

    0

    1

    0

    Magnoliales? Laurales?

    Cronquistiflora sayrevillensis (Crepet and Nixon 1998)

    flowers and fruits

    0

    0

    1

    0

    Magnoliales? Laurales?

    Detrusandra mystagoga (Crepet and Nixon 1998)

    flowers and fruits

    0

    0

    1

    0

    Magnoliales

    Endressinia brasiliana (Mohr and Bernardes-de-Oliveira 2004)

    flowers

    0

    0

    1

    0

    Magnoliales

    Futabanthus asamigawaensis (Takahashi et al. 2008)

    flower

    0

    0

    0

    1

    Laurales? Magnoliales?

    Hidakanthus (Nishida et al. 1996)

    carpels

    0

    0

    0

    1

    Assignment in Doubt

    Hyrcantha decussata (Friis et al. 2006, Leng and Friis 2006, Dilcher et al. 2007)

    flowers and leaves associated with flowers, infructescences

    0

    0

    1

    0

    Assignment in Doubt

    Hyrcantha karatscheensis (Krassilov et al. 1983)

    inflorescence

    0

    0

    1

    0

    Austrobaileyales

    Illiciospermum (Frumin and Friis 1999)

    seeds

    0

    0

    1

    0

    Nymphaeales

    Jaguariba wiersemana (Coiffard et al. 2013)

    leaves and stems

    0

    0

    1

    0

    Laurales

    Jerseyanthus calycanthoides (Crepet et al. 2005)

    flowers, stamens, staminodes, and pollen

    0

    0

    1

    0

    Laurales? Magnoliales?

    Keraocarpon (Ohana et al. 1999)

    fruits

    0

    0

    0

    2

    Magnoliales

    Lactoripollenites africanus (Zavada and Benson 1987)

    palynomorphs

    0

    0

    0

    1

    Laurales

    Lauranthus (Takahashi et al. 2001)

    flower

    0

    0

    0

    1?

    Assignment in Doubt

    Lesqueria elocata (Crane and Dilcher 1984)

    fruiting axis

    0

    0

    1

    0

    Magnoliales

    Liriodendroidea (Knobloch and Mai 1986, Frumin and Friis 1996, 1999)

    pollen and wood

    0

    0

    4

    4

    Magnoliales?

    Litocarpon beardii (Delevoryas and Mickle 1995)

    fruit with follicles

    0

    0

    0

    1

    Laurales

    Mauldinia (Drinnan et al. 1990, Eklund and Kvaček 1998, Frumin et al. 2004, Friis et al. 2006, Viehofen et al. 2008)

    flowers, inflorescences, and gynoecia

    0

    0

    2

    >2

    Assignment to Superorder in Doubt

    Metcalfeoxylon kirtlandense (Wheeler and Lehman 2000)

    wood

    0

    0

    0

    1

    Nymphaeales

    Microvictoria (Gandolfo et al. 2004)

    flowers

    0

    0

    1

    0

    Nymphaeales

    Monetianthus mirus (Friis et al. 2009)

    flower

    0

    0

    1

    0

    Assignment in Doubt

    Myricanthium (Kvacek and Eklund 2003)

    flowers

    0

    0

    2

    0

    Laurales

    Neusenia (Eklund 2000)

    flowers

    0

    0

    0

    1?

    Assignment to Superorder in Doubt

    Noferinia fusicarpa (Lupia et al. 2002)

    flowers

    0

    0

    0

    1

    Assignment to Superorder in Doubt

    Pageoxylon cretaceum (Wheeler and Lehman 2000)

    wood

    0

    0

    0

    1?

    Assignment in Doubt

    Palaeoanthella huangii (Poinar and Chambers 2005)

    flower

    0

    0

    1

    0

    Assignment in Doubt

    Paraphyllanthoxylon anazasii (Wheeler et al. 1995)

    wood

    0

    0

    0

    1

    Laurales

    Perseanthus (Herendeen et al. 1994)

    flower

    0

    0

    1

    0

    Nymphaeales?

    Ploufolia cerciforme (Sender et al. 2010)

    leaves

    0

    0

    1

    0

    Nymphaeales

    Pluricarpellatia peltata (Mohr et al. 2008)

    flowers, inflorescences, leaves, rhizomes, seeds, shoots

    0

    0

    1

    0

    Laurales?

    Pragocladus lauroides (Kvacek and Eklund 2003)

    inflorescences

    0

    0

    1

    0

    Assignment in Doubt

    Prisca reynoldsii (Retallack and Dilcher 1981, Drinnan et al. 1990)

    flowers? inflorescences?

    0

    0

    1

    0

    Assignment in Doubt

    Protomonimia kasai-nakajhongii (Nishida and Nishida 1988)

    carpels and fruits

    0

    0

    1

    0

    Nymphaeales

    Scutifolium jordanicum (D. W. Taylor et al. 2008)

    leaves and axes

    0

    0

    1

    0

    Assignment to Superorder in Doubt

    Silvianthemum suecicum (Friis 1990)

    inflorescence and fruit

    0

    0

    0

    1

    Nymphaeales

    Symphaenale futabensis (Takahashi et al. 2007)

    seeds

    0

    0

    0

    1

    Laurales?

    Virginianthus calycanthoides (Friis et al. 1994)

    flower

    0

    0

    1

    0

    Magnoliales

    Winteroxylon (Poole and Francis 2000)

    wood

    0

    0

    0

    2

    Assignment in Doubt

    Xingxueiana heilongjiangensis (Sun and Dilcher 1997)

    inflorescence

    0

    1

    0

    0

    Piperales

    Zlatkocarpus (Kvaček and Friis 2010)

    fruits, pollen, and one inflorescence

    0

    0

    2

    0


    Monocots. The following subsections constitute a brief survey of the paleontologic record of superorder Lilianae. The non-commelinid monocots are divided into the Acorales, Alismatales, Asparagales, Dioscoreales, Liliales, Pandanales, and Petrosaviales (Chase and Reveal 2009). I discuss the fossil history of commelinid monocots in a separate section.

    In 1981 Daghlian reported that the Mesozoic fossil record of monocots consisted of Alismataceae, Araceae, Arecaceae, Dioscoreaceae, Pandanaceae, Poaceae, Smilacaceae, and Zingiberaceae. Some of the controversial early records were omitted by Daghlian's early review (1981).

    The fossil history of monocots is reviewed by Stockey (2006), T. N. Taylor et al. (2009), Selena Smith (2013), and Iles et al. (2015). A compilation of advances in monocot anatomy, evo-devo, and phylogeny is available (Seberg et al. 2010).

    Students should pay close attention to a molecular-phylogenetic study published by Eguchi and Tamura in 2016, which incorporates some of the monocot fossils suggested by Iles and coworkers to calibrate cladograms. Page 1140 of Eguchi and Tamura (2016) states:

    "The divergence of monocot orders begin in the Late Jurassic period and continued throughout the Early Cretaceous in contrast to earlier studies ..."

    Friis and coworkers (2006) report a spectacular trove of indeterminate monocotyledonous angiosperm palynomorphs, flower casts, and fossilized inflorescences from the Early Cretaceous (Neocomian) of Portugal.

    Jarzen (1983), J. Müller (1984), Dahlgren et al. (1985), Uhl and Dransfield (1987), Friis (1988), Gandolfo et al. (2002), Ramanujam (2004), Friis et al. (2006), Pan et al. (2006), Scherer et al. (2006), Stockey (2006), Stockey et al. (2007), Selena Smith (2013), and Iles et al. (2015) are key sources of paleontologic data.

    The image above is the yellow floral variant of Lilium columbianum (Liliaceae, Liliales, Lilianae), which is indigenous to native prairie at the summit of Mary's Peak in the northern Coast Range of western North America.

    Monocot diversity is summarized in Dahlgren and Clifford (1982) and by Dahlgren et al. (1985). Basal monocots are reviewed by Igersheim et al. (2001). A modern synthesis of the evolutionary relationships among monocotyledonous flowering plants is published by Janssen et al. (2004).

    The "evolutionary history of the monocot flower" is published by Remizowa et al. (title, 2011).

    Michelangeli et al. (2003), Chase (2004), Chase et al. (2006), J. A. Doyle et al. (2008), Nadot et al. (2008), and Eguchi and Tamura (2016) review the phylogenetic relationships of monocots.

    Phylogenetic studies of KNOX genes and homeodomain proteins of extant grasses and eudicots suggest that KNOX Class I and KNOX Class 2 genes diverged prior to the monocot/eudicot split and reflect different evolutionary histories (Bharathan et al. 1999).

    Paula Rudall et al. (2007) provide new insight into the evolution of monocots, including assignment of Hydatellaceae to a basal position in the flowering plant crown group clade. Key studies on the reproductive biology of certain monocots which have a bearing on their adaptive radiation and origin from basal eudicot stock include work by Holloway and Friedman (2008), among others.

    Cibrián-Jaramillo and Martienssen (2009) suggest that evo-devo studies of siRNAs might shed light on divergence of monocots from eudicots. Finally, Paterson et al. (2012) review the history of polyploidy in the group including WGDs.

    Alismatales. Alismatales contain several economic plants used as a source of food (e.g. Sagittaria). Marine species known as eelgrasses are essential components of estuarine habitats occupied by commercially important fish.

    The image to the right is a clump of skunk cabbage (Lysichiton americanum, Araceae, Alismatales, Lilianae), a species indigenous to cool, coastal and montane wetlands of western North America.

    Chromosomal evolution in the Alismatales is reviewed by Feitoza et al. (2009). A second review by Furness and Banks (2010) addresses the topic of pollen evolution of the group. Finally, the systematics of alismatids is encapsulated in a review by Les and Tippery (2013).

    Molecular phylogenetic studies of cpDNA sequences by Cuenca et al. (2010) yield new insight into evolution of the Alismatales from the angle of RNA editing, which takes place following transcription of mtDNA.

    A chloroplast phylogeny has been elucidated for certain aroids (Renner et al. 2004), implicating Tertiary floristic links between east Africa, Asia, and North America. Nie et al. (2006) and Mardanov et al. (2008) offer additional insight into the evolution of aroids.

    Asparagales. A molecular phylogenetic study of several plastid and nuclear genes by Joo-Hwan Kim et al. (2010) clarifies relationships among the families of the group.

    The image to the left is a fruiting branch of Asparagus sprengeri (Asparagaceae, Asparagales, Lilianae) photographed in cultivation.

    While Paleogene and Neogene paleobotany is outside the scope of this essay, leaf cuticle studies of Miocene Asteliaceae are important first steps in calibrating phylogenies of Asparagales and related orders of monocots with roots extending back in time to the Late Cretaceous Period (Maciunas et al. 2011).

    Liliales and orchids. Records of Mesozoic fossils referable to the order Liliales consist mainly of palynomorphs deposited in sediments (J. Müller 1981). The fossil history of orchids is cloudy, but Cronquist (1981) suggests an origin of the group from lilies.

    On the right side of the page is an image of Calochortus tolmiei (Liliaceae, Liliales, Lilianae) photographed by the author in 1977 while traveling in western North America.

    Lily flowers express AP1-like MIKC-type MADS-box genes (M.-K. Chen et al. 2008).

    A study by Ramírez et al. (2007) sheds light on the time of origin of a specific orchid and its pollinator with implications toward the phylogeny and origin of monocots. In follow-up work Ramírez et al. (2011) explore peculiar asymmetries in bee and orchid pollination mutualisms possibly involving sensory behaviour.

    Based on a possibility that insect "sensory bias" might affect co-diversification with plant hosts (abstract, Ramírez et al. 2011), could studies of insect pollinator and flowering plant mutualisms from research perspectives of horizontal transmission of tool kit transposable elements shed light on underlying "evolutionary processes" in pollination ecology?

    Commelinid monocots. According to APG III (Chase and Reveal 2009), commelinid monocots consist of four orders (Arecales, Commelinales, Poales, Zingiberales) and one unplaced family (Dasypogonaceae).

    Several molecular phylogenetic studies of the commelinid plastome offer valuable insight on the matter of deep level evolutionary relationships of the group in relation to other monocots (Givnish et al. 2011), among others.

    The picture to the left is a flower of Strelitzia nicolai (Strelitziaceae, Commelinales, Lilianae) from The University of the South Pacific Botanical Garden, Suva, Fiji (photographed by the author in 1988).

    Arecales. The order Arecales contains several economically important palms used as a source of fiber (copra), food, and oil (Cocos nucifera, Elaeis guineensis, Copernicia, among others).

    A review of fossil palms of India is available (Ramanujam 2004). Additional details on the fossil history of certain palm groups may be gleaned from Uhl and Dransfield (1987). Fossil pollen belonging to this subclass may be found in sediments as old as the early Cretaceous Period.

    Remains of fossilized palms, specifically seeds and preserved stems not unlike Sabalites ungeri, are associated with bone permineralizations of immature dinosaurians in the Upper Cretaceous Aguja Formation of southwestern North America (Manchester et al. 2010).

    Students of fossil palms should be cautioned that an early (Late Jurassic) record of Palmoxylon pristina and Palmoxylon simperi (Tidwell et al. 1970) is in doubt. The petrified log fragments in question probably eroded from overlying Paleogene rocks.

    A taphonomic study of fossil palms is available (Marmi et al. 2010). Upper Cretaceous records of palm fruits are known for the genus Nypa (El-Soughier et al. 2011). The aforementioned studies do not obviate the possibility that palm permineralizations will be discovered in Malm rocks.

    Poales. Members of the order Poales are among the most economically important plants known. The major cereal grains of the Poales are oats (Avena), bamboo (Bambusa), rye (Elymus), barley (Hordeum), rice (Oryza), millet (Sorghum), and wheat (Triticum).

    Metaphase I of meiosis in a squashed microspore mother cell of Joinvillea plicata (Joinvilleaceae, Poales, Commelinidae) is imaged to the right, × 2000. Eighteen pairs of chromosomes (2n = 36) are visible in the squashed microspore mother cell. Living tissues, cells, and chromosomes of a Joinvillea clone growing along a roadside on the island of Viti Levu, Fiji were field-fixed in a mixture of chloroform, 100% ethanol, and glacial acetic acid on 11 April 1986. A staining technique developed by R. Snow (1963, Stain Technology 38: 9-13) was used to prepare the tissue for phase-contrast light microscopy. Voucher specimens of J. M. Miller No. 971 are deposited at the Bishop Museum (BISH) and Rancho Santa Ana Botanic Garden (RSA).

    Joinvilleaceae are monocotyledonous flowering plants (Tomlinson and A. C. Smith 1970) that share vegetative morphology reminiscent of the enigmatic and controversial Triassic fossil Sanmiguelia lewisii. Joinvilleas possess a primitive morphotype with perfect and complete flowers having petals, sepals, stamens, and a trilocular ovary. Joinvilleaceae are classified by some botanists in Flagellariaceae which is allied to Restionaceae, comprised of Czaja's primary monocots.

    A draft analysis of the cpDNA plastome for Joinvillea plicata is available (Leseberg and Duvall 2009).

    Hydatellaceae (Rudall et al. 2007), a family classified by Cronquist (1981) in the Commelinidae, are discussed in the section on basal angiosperms.

    Kåre Bremer (2002) and Linder et al. (2007) are two key articles on the Mesozoic fossil history and biogeography of commelinid monocots. Whipple et al. (2007) offer important insight on the origin of grasses and the grass lodicule from studies of MIKC-type MADS-box B gene expression of Joinvilleaceae, Streptochaeta angustifolia, a basal grass species, and several derived taxa of Poaceae.

    The molecular systematics of bamboos and related genera of Poaceae is published in a paper by Hisamoto et al. (2008). MIKC-type MADS-box gene expression and evolution in grasses is addressed in papers by Preston and Kellogg (2007) and Preston et al. (2009), among others. Based on detailed genomic studies of Sorghum bicolor, paleopolyploidy about 70 MYA preceded divergence of the millet and rice clades (Paterson et al. 2009).

    Fossil restionaceous pollen has been reported from late Cretaceous sediments (Dahlgren and Clifford 1982). Roots of the Poales, discernable from widespread occurrences of Graminidites (Poales incertae cedis) in dinosaur coprolites and sediments, are traceable to the Maastrichtian Age (Srivastava 2011).

    Zingiberales. The order Zingiberales contains several economically important plants including bananas, ginger, and pineapple.

    The image the left is an inflorescence of a ginger plant Zingiber zerumbet, an aboriginal introduction to the high islands of the South Pacific (photographed by the author).

    Floral tool kit plant biology of gingers and related monocots is an ongoing topic of gene expression research by Chelsea Specht and coworkers (Bartlett and Specht 2010, Yockteng et al. 2013).

    The fossil history of bananas (Musa) is discussed by Manchester and Kress (1993). Bromeliad biogeography and phylogenetics is summarized by Givnish et al. (2004). Floral development of the Zingiberales is reviewed by Kirchoff et al. (2009).

    Gingers are host plants for certain hispine beetles. Ichnofossils allow paleobiologists to infer the existence of extinct phytophagous hispine beetles (García-Robledo and Staines 2008). Wilf et al. (2000) review the fossil history of zingiberids and rolled leaf hispine beetles.

    Table 8 is the Mesozoic fossil record of monocots (superorder Lilianae). Neocomian records for monocots are among the oldest known angiosperm megafossils (T. N. Taylor et al. 2009) paralleling the situation seen in basal angiosperms and magnoliids suggesting unresolved deep divergences.


    Table 8. Mesozoic Stratigraphic Distribution of Monocots.

    Order

    Scientific Name and Publication

    Fossilized Remains

    Malm - Jurassic

    Neocomian - Cretaceous

    Gallic - Cretaceous

    Senonian - Cretaceous

    Arales

    Cobbania corrugata (Stockey et al. 2007)

    whole plants, stems, leaves, roots

    0

    0

    0

    1

    Liliales?

    Cretovarium (Stopes and Fujii 1910)

    flower

    0

    0

    0

    1

    Arecales

    Deccananthus savitrii (Chitaley and Kate 1974)

    flowers and fruits

    0

    0

    0

    1

    Poales

    Graminidites (Srivastava 2011)

    pollen

    0

    0

    0

    1

    Triuridales

    Mabelia archaia (Gandolfo et al. 2002)

    flower

    0

    0

    1

    0

    Triuridales

    Mabelia connatifila (Gandolfo et al. 2002)

    flower

    0

    0

    1

    0

    Arales

    Mayoa portugallica (Friis et al. 2004)

    inflorescence axis with pollen

    0

    1

    0

    0

    Arecales

    Mauritiidites (Herngreen et al. 1996)

    pollen

    0

    0

    0

    1

    Zingiberales

    Musa cardiosperma (Jain 1963)

    fruits and seeds

    0

    0

    0

    1

    Triuridales

    Nuhliantha nyanziana (Gandolfo et al. 2002)

    male flower

    0

    0

    1

    0

    Arecales

    Nypa burtinii (El-Soughier et al. 2011)

    fruits and seeds

    0

    0

    0

    1

    Arecales

    Palmoxylon cliffwoodensis (Daghlian 1981)

    wood

    0

    0

    0

    1

    Arecales

    Pandanites (Scherer et al. 2006)

    pollen

    0

    0

    0

    1

    Arecales

    Pandanus (Jarzen 1983)

    pollen

    0

    0

    0

    >1?

    Alismatales

    Pennipollis (Penny 1988, Hughes 1994)

    palynomorphs

    0

    1

    0

    0

    Alismatales

    Pennistemon (Friis et al. 2000)

    inflorescences with pollen

    0

    1

    0

    0

    Arecales

    Sabal bigbendense (Manchester et al. 2010)

    seeds and stems

    0

    0

    0

    1

    Arecales

    Sabal bracknellense (Manchester et al. 2010)

    seeds and stems

    0

    0

    0

    1

    Arecales

    Sabalites longirhachis (Marmi et al. 2010)

    leaves, roots, stems

    0

    0

    0

    1

    Arecales? Pandanales?

    Shuklanthus superbum (Verma 1958)

    flowers and fruits

    0

    0

    0

    1

    Arecales

    Spinozonocolpites (Herngreen et al. 1996)

    pollen

    0

    0

    0

    1

    Zingiberales

    Spirematospermum chandlerae (Friis 1988)

    fruits, seed

    0

    0

    0

    1

    Arecales? Pandanales?

    Tricoccites trigonum (Chitaley 1956)

    flowers and fruits

    0

    0

    0

    1

    Arecales? Pandanales?

    Viracarpon (Nambudiri and Tidwell 1978)

    flowers and fruits

    0

    0

    0

    1


    Eudicots. Eudicots assignable to the Ranunculanae are traceable to the Barremian Age (Neocomian Epoch) of the Lower Cretaceous Period (G. Sun et al. 2011). Paleobotanical highpoints of the eudicots within Angiosperm Phylogeny Group-constructs are reviewed by D. W. Taylor and Hickey (1996), T. N. Taylor et al. (2009), Friis et al. (2011), Barral et al. (2013), Jud and Hickey (2013), J. A. Doyle and Upchurch (2014), and Jud (2014).

    The image on the right side of this page is reproduced from Jud and Hickey (Figure 3, 2013) with the written permission of Professor Judy Jernstedt, Editor-in-chief of the American Journal of Botany, copyright ©2013.

    "Potomacapnos apeleutheron gen. et sp. nov. 3, USNM 559298 (Holotype) showing two lobed leaflets with reticulate venation, intramarginal vein, and glandular teeth. The right leaflet has two major lobes and three lateral lobes. The left leaflet has one major lobe and one minor lobe preserved. The left leaflet is folded under and twisted about its axis 180°. It is 1–2 mm deeper in the matrix than the right leaflet. L: Major lobe, ll: lateral lobe. Scale bar = 5 mm."

    Eudicots consist of superorder Buxanae (a single order Buxales), superorder Proteanae (one order, Proteales), and superorder Ranunculanae consisting of the Ranunculales. Superorder Trochodendranae (comprised of the order Trochodendrales) is somehow left out of the paper by Chase and Reveal, but is clearly intended (page 125, Figure 1, 2009).

    Superorder Trochodendranae Takhtajan ex Reveal, Phytologia 79(2): 71, 29 Aug 1995, is a valid name (Reveal 1995). Superorder Ceratophyllanae and its only order Ceratophyllales are sister to the eudicots and unplaced (Chase and Reveal 2009).

    The evolutionary history, flower structure, fossil history, and phylogenetic relationships of eudicots, core eudicots, and Ceratophyllanae, among other groups, is reviewed by Drinnan et al. (1994), D. E. Soltis et al. (2003), Judd and Olmstead (2004), Magallón (2004), L. Chen et al. (2007), Worberg et al. (2007), Dilcher and H. Wang (2009), Gomez et al. (2009), W. Wang et al. (2009), Endress (2010), and Jun Wang et al. (2013), among others.

    The kodachrome to the left is the lower eudicot Adonis amurensis (Ranunculaceae, Ranunculales, Ranunculanae) photographed by the author.

    A pivotal biochemical study of the sacred lotus genome by Yun Wang and coworkers (2013) reveals no trace of a "γ triplication," which is a key marker in the evolutionary history of eudicots and monocots (Jiao et al. 2011, Jiao et al. 2012, P. S. Soltis and D. E. Soltis 2016). This study places Nelumbo nucifera as an [auto- or allo-?]tetraploid in a basalmost position among the crown group of extant eudicots.

    Students of angiosperm floral evolution should focus on Figure 1 on page 559 of Yun Wang et al. (2013). Based on this analysis but without fossil calibration, Nelumbonaceae diverged from the whole of eudicots more than 140 MYA, at or near the Jurassic-Cretaceous boundary but following the fossil-calibrated split from monocots (Eguchi and Tamura 2016). If proven correct by way of paleobotanical evidence than how can Chanderbali et al. (2016) justify the statement on the first line of the paper?

    Omission of any discussion of the important Nelumbo nucifera genome study by Yun Wang et al. (2013) in a review of the history of angiosperm WGDs (P. S. Soltis and D. E. Soltis 2016) is strange and perplexing, especially since both research labs publish studies in The Plant Journal.

    Key phylogenetic and evo-devo studies of eudicots are published by Hoot et al. (1999), Magallón et al. (1999), Fishbein et al. (2001), D. E. Soltis et al. (2003), Chaw et al. (2004), S. Kim et al. (2004), R.-Q. Li (2004), C. L. Anderson et al. (2005), Zahn et al. (2005), De Bodt et al. (2006), Endress and Mathews (2006), Barakat et al. (2007), Ren et al. (2007), Ronse De Craene (2007), Hilu et al. (2008), Ronse De Craene (2008), Endress (2010), Yellina et al. (2010), and Pérez-Gutiérrez et al. (2015), among others.

    A supposed "unidirectional model of ovary position evolution" is called into question by an elegant phylogenetic study that incorporates developmental data (page S252, D. E. Soltis et al. 2003). Endress (2010) proposes changes to the classification of major eudicot groups based on ovular features specifically of the nucellar type.

    Phylogenetic analyses of the AP1/FUL gene lineage in flowering plants by Litt and Irish (2003) suggest that a gene duplication coincides with diversification and radiation within the ranunculid lineage. Further, Litt and Irish propose that one or more gene duplications in the AP1 MIKC-type MADS-box gene lineage leading to the euAP1 clade might have played a role in the evolution of eudicot floral structure.

    Evolutionary development and phylogeny of the AP3/TM6 gene lineage in eudicots is reviewed by Hileman and Irish (2009). Conclusions reached by Bharti Sharma et al. (2011) on evo-devo studies of paralogs of AP3 in Aquilegia suggest that:

    "... the AqAP3-3 lineage underwent progressive subfunctionalization within the order Ranunculales, ultimately yielding a specific role in petal identity that has probably been conserved, in stark contrast with the multiple independent origins predicted by botanical theories."

    The above statement is from the abstract of Bharti Sharma, C. Guo, H. Kong, and E. M. Kramer, (2011), Petal-specific subfunctionalization of an AP3 paralog in the Ranunculales and its implications for petal evolution. New Phytologist 191(3): 870-883.

    Zahn et al. (2005) report several MIKC-type MADS-box E gene duplications within the AGL2, AGL3, AGL4, and AGL9 molecular clades of the eudicot lineage, including the branch leading to monocots. Duplications of the TCP family of genes, specifically CYC, predate divergence of core eudicots (Howarth and Donoghue 2006).

    Buxanae. The Mesozoic fossil history of the eudicot order Buxales is reviewed by T. N. Taylor et al. (2009).

    Buxales and other fossil eudicots figure prominently in studies on Cretaceous extinctions (Heimhofer et al. 2005) and phylogenetics (C. L. Anderson et al. 2005).

    Ceratophyllanae. Once classified as magnoliids (Cronquist 1981), Ceratophyllanae are represented in the Mesozoic fossil record by Donlesia dakotensis from the North American Dakota Formation (Dilcher and H. Wang 2009), and by the Barremian fossil plant Montsechia vidalii (Bernard Gomez et al. 2015).

    "... the fossil angiosperm presented here [Montsechia], raises questions centered on the very early evolutionary history of angiosperms. The importance of very early aquatic flowering plants, perhaps basal to all angiosperms [they are not, in my opinion], as previously proposed [G. Sun et al. 1998], merits serious consideration and reevaluation" (page 10987, Bernard Gomez et al. 2015, comments in [brackets] are mine).

    Iwamoto et al. (2015) detail certain aspects pertaining to phylogenetics and morphologies of extant Ceratophyllum demersum (Ceratophyllaceae, Ceratophyllales, Ceratophyllanae).

    The figure on the right is from Akitoshi Iwamoto et al. (2015), which is reproduced by written permission of Professor Iwamoto of Tokyo Gakugei University and Kodan-sha [4-1-1 Nukui Kita-machi, Koganei-shi, Tokyo 184-8501, JAPAN].

    I thank the American Journal of Botany Editorial Office for coordinating the necessary written permissions from the publisher in Japan.

    "FIGURE 1 Ceratophyllum demersum L. (A) Shoot in aquatic environment. (B) Vegetative buds covered with prophylls, in the axil of a leaf. (C) Staminate flower consisting of numerous stamens and surrounding bracts. (D) Pistillate flower consisting of only one pistil with long stigma and surrounding bracts. b, bract; l, leaf; p, prophylls; st, stamen; sti, stigma. Scale bars = 1 cm (A); 500µm (B-D). Photographs are from Akitoshi Iwamoto (2012) with permission," copyright ©2012 Kodan-sha, Tokyo, Japan.

    The Iwamoto team discusses vegetative phyllotaxis of this plant and scanning electron microscopy of developing staminate and pistillate flowers offers a window on floral development in Ceratophyllum demersum (Akitoshi Iwamoto et al. 2003).

    Ceratophyllales have been discussed as key evolutionary players in debates on the origin and ancestry of flowering plants (D. H. Les 1988, D. H. Les et al. 1991). Interestingly, branched pollen tubes are observed in Ceratophyllum (D. H. Les 1988, 1993).

    "Based on its unparalleled morphological features, D. H. Les (1988) suggested that the genus [Ceratophyllum] is [was] closest to ancestral angiosperms" (Introduction on page 1578, Akitoshi Iwamoto et al. 2015, the words in [brackets] are mine).

    The Barremian fossil plant Montsechia vidalii has been known to paleobotanists for several decades as an aquatic liverwort assigned to Jungermanniales. Affinities of Montsechia with angiosperms was suggested later (Martín-Closas 2003).

    "... Ceratophyllaceae are truly 'living fossils' and represent plants which probably diverged from some of the earliest angiosperm progenitors ..." (Conclusions on page 341, D. H. Les 1988).

    The diagram below was redrawn from Figure 4 on page 341 of D. H. Les (1988), "Hypothetical phylogenetic relationship of Ceratophyllales, Nymphaeales, and modern monocots and dicots." I colorized and changed the font of the typescript to conform to gigantopteroid web page style.

    Proteanae. Proteas are now included with platanoids (T. N. Taylor et al. 2009) and Nelumbonaceae (Gandolfo and Cuneo 2005) in the order Proteales. Fossil Protea pollen are known from the subantarctic islands (Wanntorp et al. 2011).

    Platanoids (sycamores and relatives) have a rich Cretaceous fossil history (Upchurch and Wolfe 1987, Friis et al. 1988, Crane et al. 1993, Magallón-Puebla et al. 1997, Upchurch and Wolfe 1987, Mindell et al. 2006, Maslova 2010, Golovneva 2010, H. Wang et al. 2011, among others).

    The foliage genus Sapindopsis (Hickey and J. A. Doyle 1977) is one of the best known examples of late Mesozoic platanoid foliage (T. N. Taylor et al. 2009). Permineralized Cretaceous woods, Icacinoxylon and Plataninium (Wheeler and Lehman 2000, Oakley and Falcon-Lang 2009), might belong to extinct Proteales but anatomical connections with detached foliage, flowers, and fruits are lacking.

    A new classification system of fossil platanoids is proposed by Maslova (2010), which is at variance with the older APG II classification scheme. Surprisingly, Maslova (2010) neglects to compare these novel ideas with the more recent APG III system (Chase and Reveal 2009).

    Ranunculanae. The Mesozoic fossil history of the eudicot order Ranunculales is reviewed by Krassilov (1997), Krassilov and Golovneva (2001), Krassilov and Golovneva (2004), von Balthazar et al. (2005), Gomez et al. (2009), and T. N. Taylor et al. (2009), among others.

    The oldest fossil ranunculid eudicot, Leefructus, is 123 to 124 million years old, which is the Barremian Age of the Lower Cretaceous Period (G. Sun et al. 2011).

    On the left side of the page is an image of Platystemon californicus (Papaveraceae, Papaverales, Ranunculanae) photographed by the author in the 1970s while traveling in western North America. Does the flower in the center of the image belong to the same plant?

    Perianth evolution in Ranunculales is discussed in a study by Rasmussen et al. (2009). The genus Aquilegia (Ranunculaceae, Ranunculales, Ranunculanae) has become a model organism for floral organ evo-devo (Kramer 2009, Bharti Sharma et al. 2011).

    Trochodendranae. Cretaceous fossils referable to the Trochodendrales are described by Crane (1989). The paleontology of the group is summarized in T. N. Taylor et al. (2009).

    I cast the available data on the fossil history of eudicots (excluding core eudicots) and Ceratophyllanae into Table 9. Please note that the number in each cell represents the number of species or genera as the case may be.


    Table 9. Mesozoic Stratigraphic Distribution of Eudicots and Ceratophyllanae (Except Core Eudicots).

    Order

    Scientific Name and Publication

    Fossilized Remains

    Malm - Jurassic

    Neocomian - Cretaceous

    Gallic - Cretaceous

    Senonian - Cretaceous

    Proteales

    undescribed (Dettmann and Jarzen 1998)

    pollen

    0

    0

    0

    >2?

    Proteales

    unclassified platanoid leaves and fertile structures (Upchurch and Wolfe 1987, Mindell et al. 2006)

    leaves, flowers, and inflorescences

    0

    0

    >2

    >2

    Proteales

    Nelumbonaceae under study (Gandolfo and Cuneo 2005)

    leaves and detached fruits

    0

    0

    0

    1

    Trochodendrales

    unclassified leaves (Upchurch and Wolfe 1987)

    leaves

    0

    0

    >2

    >2

    Assignment in Doubt

    Allonia decandra (Magallón-Puebla et al. 1996)

    flower

    0

    0

    0

    1

    Proteales

    Beaupreaidites (Wanntorp et al. 2011)

    pollen

    0

    0

    0

    1

    Ranunculales

    Callicrypta chlamydea (Krassilov and Golovneva 2004)

    flowers

    0

    0

    1

    0

    Ranunculales?

    Caspiocarpus paniculiger (Krassilov 1997)

    flowers

    0

    0

    1

    0

    Ceratophyllales

    Donlesia dakotensis (Dilcher and H. Wang 2009)

    fruits

    0

    0

    1

    0

    Proteales

    Exnelumbites callejasiae (Estrada-Ruiz et al. 2011)

    leaves

    0

    0

    0

    1

    Ranunculales

    Freyantha sibirica (Krassilov and Golovneva 2001)

    staminate inflorescence and flowers

    0

    0

    1

    0

    Trochodendrales

    Joffrea (Crane 1989)

    leaves and winged fruits

    0

    0

    0

    >2

    Ranunculales?

    Klitzschphyllites choffatii (Gomez et al. 2009)

    leaves

    0

    0

    1

    0

    Ranunculales

    Leefructus (G. Sun et al. 2011)

    inflorescences and leaves

    0

    1

    0

    0

    Ranunculales

    Macclintockia (Moiseva 2011)

    leaves

    0

    0

    0

    3

    Ceratophyllales

    Montsechia vidalii (B. Gomez et al. 2015)

    fruits and stems

    0

    1

    0

    0

    Trochodendrales

    Nordenskioldia (Crane 1989)

    leaves, inflorescences, fruits, and fruitlets, shoots

    0

    0

    0

    1

    Assignment in Doubt

    Normanthus (Schönenberger et al. 2001, Friis et al. 2003)

    inflorescence

    0

    0

    1

    0

    Proteales

    Paraprotophyllum (Golovneva 2010)

    leaves

    0

    0

    1

    0

    Proteales

    Platananthus (Friis et al. 1988)

    inflorescence

    0

    0

    1

    0

    Proteales

    Platanocarpus brookensis (Crane et al. 1993)

    pistillate inflorescences and infructescences

    0

    0

    1

    0

    Proteales

    Platanocarpus marylandensis (Friis et al. 1988)

    flowers and fruits

    0

    0

    1

    0

    Ranunculales

    Potomacapnos apeleutheron (Jud and Hickey 2013)

    leaves

    0

    0

    1

    0

    Proteales

    Proteacidites (Wanntorp et al. 2011)

    pollen

    0

    0

    0

    2

    Proteales

    Quadriplatanus georgianus (Magallón-Puebla et al. 1997)

    staminate and pistillate flowers

    0

    0

    0

    1

    Ranunculales

    Sagaria cilentana (Bravi et al. 2010)

    inflorescence

    0

    0

    1

    0

    Proteales

    Sapindopsis (Hickey and J. A. Doyle 1977)

    leaves

    0

    0

    >2

    >2

    Ranunculales

    Teixeiraea lusitanica (von Balthazar et al. 2005)

    male flower, flower buds, and pollen

    0

    0

    1

    0


    Core eudicots, rosids, and asterids. According to APG III (2009) core eudicots are comprised of superorder Myrothamnanae consisting of a single order Gunnerales, the unplaced order Saxifragales, superorder Rosanae (many rosid orders and families of fabids and malvids) and the enigmatic Vitales, and the unplaced family Dilleniaceae. The latest phylogenetic analysis of this group suggests that "both superrosids and superasterids arose in as little as five million years," during the Cretaceous Period (abstract, Moore et al. 2010).

    In addition, core eudicots include superorder Berberidopsidanae (the single order Berberidopsidales), superorder Caryophyllanae (one order, Caryophyllales), superorder Santalanae consisting of the order Santalales and several asterid, campanulid, and lamiid orders classified in the superorder Asteranae (Chase and Reveal 2009).

    During the Cretaceous Period certain core eudicots were important floristic elements in many localities as judged from the common occurrence of Normapollis. Albian compression floras contain a high frequency of platanoid leaves and definitive leaf-forms which are classifiable to Trochodendrales (Upchurch and Wolfe 1987).

    Rosids (fabids and malvids) and asterids (lamiids and campanulids) are discussed in essay sections separate from the remaining core eudicots.

    Two MIKC-type MADS-box B gene duplications within the core eudicots probably generated the euAP1, euFUL, and core eudicot FUL-like clade. The AP1/FUL gene duplications potentially generated novel C-terminal motifs in euAP1 proteins with new functions possibly leading to fixation of general eudicot floral structure (Litt and Irish 2003) or further diversification (Shan et al. 2007).

    Caryophyllanae. The betalain containing Caryophyllanae (Clement et al. 1994), a possible distinct evolutionary line of core eudicot flowering plants characterized by unique sieve tube plastid anatomy (Behnke 1994) has been reviewed from the perspective of perianth biology (Brockington et al. 2009).

    Molecular systematics of the Caryophyllales is under study including work published by Cuénoud et al. (2002), Brockington et al. (2009), and Brockington et al. (2011), among others.

    The slide to the left is a cluster of inflorescences of a shrub of Eriogonum torreyanum (Polygonaceae, Caryophyllales, Caryophyllanae), a species indigenous to the Harney Basin of western North America, photographed by the author.

    Cevallos-Ferriz et al. (2008) described a permineralized core eudicot infructescence from the late Cretaceous (Campanian) Cerro del Pueblo Formation of Mexico, which is assignable to Phytolaccaceae.

    Myrothamnanae. The genus Gunnera (Gunnerales) is represented in the Cretaceous record of angiosperms by an extensive pollen record (Jarzen 1980). Placement of Gunnerales by D. E. Soltis et al. (page 466, 2003) "as sister to all other eudicots has important implications for floral evolution."

    Santalanae. Several flowering plant families are parasitic on other vascular plants. According to APG IV (2016), these are now better placed as superasterids. Among these Misodendraceae of the order Santalales appeared in aerial canopies of Cretaceous forests some 80 MYA (Vidal-Russell and Nickrent 2008).

    Santalales are represented in the fossil record of Cretaceous woods represented by Agujoxylon olacaceoides (Wheeler and Lehman 2000). Thomas N. Taylor et al. (2009) reviews the paleontologic record of sandalwoods and relatives in the Santalales.

    Saxifragales. Roots of the unplaced core eudicot order Saxifragales may be traced back to the Cretaceous Period (T. N. Taylor et al. 2009). Mesozoic fossil forms are Dewalquea pulchella (Nichols and Jacobson 1982), Aquia brookensis (Crane et al. 1993), Androdecidua endressii (Magallón et al. 2001), and Microaltingia apocarpela (Zhou et al. 2001), among others.

    The molecular systematics and ancient radiations of Saxifragales is resolved in a paper by Jian et al. (2008).

    On the right side of the page is an image of Saxifraga retusa (Saxifragaceae, Saxifragales, unplaced core eudicot) photographed by the author in the 1991 while visiting the University of British Columbia Botanical Garden.

    Table 10 outlines the Mesozoic stratigraphic record of fossil core eudicots and unplaced orders (except rosids and asterids).


    Table 10. Mesozoic Stratigraphic Distribution of Core Eudicots and Unplaced Orders (Except Rosids and Asterids).

    Order

    Scientific Name and Publication

    Fossilized Remains

    Malm - Jurassic

    Neocomian - Cretaceous

    Gallic - Cretaceous

    Senonian - Cretaceous

    Santalales

    Agujoxylon olacaceoides (Wheeler and Lehman 2000)

    wood

    0

    0

    0

    1

    Saxifragales

    Androdecidua endressii (Magallón et al. 2001)

    floral fragments with stamens

    0

    0

    0

    1

    Saxifragales

    Aquia brookensis (Crane et al. 1993)

    staminate inflorescences

    0

    0

    1

    0

    Caryophyllales

    Archaeamphora longicervia (H. Li 2005)

    plant fragments

    0

    0

    0

    1

    Caryophyllales

    Coahuilacarpon phytolaccoides (Cevallos-Ferriz et al. 2008)

    infructescence

    0

    0

    0

    1

    Saxifragales

    Dewalquea pulchella (Nichols and Jacobson 1982)

    leaves

    0

    0

    1

    0

    Gunnerales

    Gunnera (Jarzen 1980)

    pollen

    0

    0

    1

    1

    Saxifragales

    Hamatia (Pederson et al. 1994)

    flower and inflorescence

    0

    0

    1

    0

    Saxifragales

    Microaltingia apocarpela (Zhou et al. 2001)

    pistillate inflorescences and infructescences

    0

    0

    1

    0

    Saxifragales

    Tarahumara (Hernandez-Castillo and Cevallos-Ferriz 1999)

    inflorescence

    0

    0

    0

    1


    Rosanae. Superorder Rosanae consists of the malvid and fabid clades of rosids and the order Vitales (Chase and Reveal 2009). The extant model seed plant species Arabidopsis thaliana and Carica papaya are probably the two best studied malvids from the standpoint of developmental genetics.

    Using fossil calibration points the molecular phylogenetic paper by Beilstein et al. (2010) suggests a Miocene origin of Arabidopsis thaliana and an uppermost Cretaceous origin of the Brassicales. Coevolution of mustards and pierid butterflies first proposed by Ehrlich and Raven (1964) is demonstrable (Beilstein et al. 2010).

    Crepet (1996) offers an insightful review of the tricolpates (tricolpate is a word describing palynomorphs with three furrows [colpae]), many (not all flowering plants with tricolpate pollen are rosids) are now known to be rosids.

    The kodachrome to the left is a flowering branch of a shrub of Sophora formosa (Fabaceae, Fabales, Rosanae) from the Pinaleño Mountains of southwestern North America (photographed by the author).

    Advances in our understanding of Cretaceous rosid phylogeny and radiation appear in work published by Sytsma et al. (2002), Hall et al. (2004), Wojciechowski et al. (2004), Davis et al. (2005), L.-B. Zhang (2006), X.-Y. Zhu et al. (2007), Jian et al. (2008), Bello et al. (2009), and Hengchang Wang et al. (2009), among others.

    Robert Jansen et al. (2011) report numerous transfers of rpl22, a plastidic sequence, to the nuclear genomes of several rosids.

    Volume 260, Numbers 2-4 of Plant Systematics and Evolution (2006) is devoted to a review of the evolution, fossil history, morphology, and phylogenetic relationships of rosids. Specific papers in Numbers 2-4 of Volume 260 of possible interest are by von Balthazar et al. (2006), Endress and Friis (2006), Endress and Mathews (2006), Hermsen et al. (2006), Mathews and Endress (2006), and Schönenberger and von Balthazar (2006), among others.

    Malvids. Plant biologists who study angiosperms from biochemical, evo-devo, and genomic research perspectives are probably most familiar with Arabidopsis thaliana, Populus trichocarpa, and Theobroma cacao, which are classified as malvids according to APG III.

    On the right side of the page is an image of Hibiscus hirtus (Malvaceae, Malvales, Rosanae) photographed in cultivation by the author in 1985.

    De Bodt et al. (2006) studied MIKC-type MADS-box gene expression analysis and compared the promoter sequences of two malvid species, Arabidopsis thaliana and Populus trichocarpa, using phylogenetic methods. While the analysis by De Bodt et al. (2006) has no direct bearing on the origin of angiosperms (this was not the intent of their research project) it reveals that TF binding sites of these two eudicots have diverged widely, probably due to gene duplications, loss of function of certain duplicated genes to form pseudogenes, mutations, or isoform genesis.

    Table 11 outlines the Mesozoic stratigraphic distribution of the malvid clade of rosids.


    Table 11. Mesozoic Stratigraphic Distribution of the Malvid Clade of Rosids.

    Order

    Scientific Name and Publication

    Fossilized Remains

    Malm - Jurassic

    Neocomian - Cretaceous

    Gallic - Cretaceous

    Senonian - Cretaceous

    Malvales

    Bombacoxylon langstoni (Wheeler and Lehman 2000)

    wood

    0

    0

    0

    1

    Brassicales

    Dressiantha bicarpellata (Gandolfo et al. 1998)

    flowers

    0

    0

    1

    0

    Assignment in Doubt

    Elsemaria kokubunii (Nishida 1994)

    fruit

    0

    0

    0

    1

    Myrtales

    Esquieria (Friis et al. 1992, Takahashi et al. 1999)

    flowers

    0

    0

    0

    2

    Malvales

    Javelinoxylon multiporosum (Wheeler et al. 1994)

    wood

    0

    0

    0

    1

    Geraniales

    Sarysua pomona (Krassilov et al. 1983)

    inflorescence

    0

    0

    1

    0

    Myrtales

    Trapago angulata (Stockey and Rothwell 1997)

    flower and fruit

    0

    0

    0

    1


    Fabids. The fossil history and phylogenetic systematics of fabids is discussed by Manchester (1987), Donoghue and J. A. Doyle (1989), Crepet et al. (1992), Chen et al. (1999), Zhou et al. (2001) and Takahashi et al. (2008), among others.

    Witch hazels, sweet gums, wax myrtles, beeches, alders, oaks, and beefwoods once classified by Cronquist (1981) in subclass Hamamelidae, and Celastrales, are now placed in the fabid clade of superorder Rosanae together with Fabales and Rosales (Chase and Reveal 2009).

    On the left side of the page is an image of Cercocarpus betuloides (Rosaceae, Rosales, Rosanae) photographed by the author in 1976 while traveling in western North America.

    Some of the best known examples of fossil flowers (see the images at the beginning of this essay and below) are casts and three-dimensional petrifactions of rosids from the Lower Cretaceous Dakota Formation Rose Creek locality. Many of these fossil flowers were comparatively large and pentamerous, possibly allied with the Celastrales (Basinger and Dilcher 1984).

    Several problematic morphotype genera of detached leaves and pollen from the Maastrichtian Age possibly belonging to fabids are reported in the literature (Manchester 1987, among others). According to Friis et al. (2006), Normapolles pollen have been found in situ in several fossilized flowers of primitive beeches and oaks.

    The sandstone cast pictured on the right hand side of this page is an indeterminate pentamerous rosid flower (Celastrales, Rosanae) collected by Professor David L. Dilcher from the Lower Cretaceous Dakota Formation of North America. The image was captured in 1981 while the author was visiting Indiana University.

    Phylogenetic relationships within extant genera classified in the birch family (Betulaceae) ascertained from studies of rbcL, ITS, and morphology are congruent with paleobotanical and paleoecological data (Chen et al. 1999).

    Based on studies of two nuclear- and ten plastid gene loci by S.-D. Zhang et al. (2011) the Rosales are probably monophyletic. Paleobotanical calibration of molecular phylogenetic analyses of rosids and other eudicots are needed especially in view of the rich and diverse fossil record of the group.

    Woody, often tree-like fabids, malvids and other rosids were evidently common in Cretaceous floras including evolutionary lines leading to Paleogene and Neogene species of beeches (including Nothofagus, a favorite of biogeographers), birches, hazelnuts, oaks, and walnuts (Friis et al. 2006, Manos et al. 2007, Golovneva 2008, Narita et al. 2008, Oh and Manos 2008, Tschan et al. 2008, X. Wang 2008, Y.-H. Wang et al. 2009, among others).

    Table 12 outlines the Mesozoic fossil history, at least of definitive reproductive remains of the fabid clade of rosids.


    Table 12. Mesozoic Stratigraphic Distribution of the Fabid Clade of Rosids.

    Order

    Scientific Name and Publication

    Fossilized Remains

    Malm - Jurassic

    Neocomian - Cretaceous

    Gallic - Cretaceous

    Senonian - Cretaceous

    Assignment in Doubt

    undescribed rosids (Herendeen et al. 1999)

    indeterminate flowers and fruits

    0

    0

    0

    >2?

    Rosales

    undescribed rosid (Crepet and Nixon 1996)

    stamens

    0

    0

    1

    0

    Assignment in Doubt

    undescribed rosids (Takahashi et al. 1999)

    indeterminate flowers and fruits

    0

    0

    0

    >2?

    Malpighiales?

    Agapitocarpus (Leng et al. 2005)

    fruits

    0

    0

    0

    1

    Fagales

    Alnipollenites (Miki 1977)

    palynomorphs

    0

    0

    0

    1

    Fagales

    Antiquacupula (Herendeen et al. 1995, Sims et al. 1998)

    flowers and inflorescences

    0

    0

    0

    1

    Fagales

    Antiquocarya (Friis 1983)

    fruits

    0

    0

    0

    1

    Assignment in Doubt

    Aquacarpus hirsutus (Raunsgaard-Pedersen et al. 2007)

    pistillate floral fragments

    0

    0

    1

    0

    Fagales

    Archaefagacea futabensis (Takahashi et al. 2008)

    flower, fruit, pollen

    0

    0

    0

    1

    Fagales

    Archamamelis bivalvis (Endress and Friis 1991)

    flower

    0

    0

    0

    1

    Rosales

    Asterocelastrus cretacea (Krassilov and Pacltova 1989)

    fruits

    0

    0

    1

    0

    Fagales

    Bedellia (Sims et al. 1999)

    flowers and fruits

    0

    0

    0

    1

    Fagales

    Betulaceoipollenites (Miki 1977, X.-J. Sun et al. 1979)

    palynomorphs

    0

    0

    0

    1

    Fagales

    Betulaepollenites (Miki 1977)

    palynomorphs

    0

    0

    0

    1

    Fagales

    Budvaecarpus (Knobloch and Mai 1986)

    flower

    0

    0

    1

    0

    Fagales

    Caryanthus (Friis 1983)

    flowers and fruits

    0

    0

    0

    3

    Assignment in Doubt

    Chitaleypushpam mohgaoense (Paradkar 1973)

    flowers and fruits

    0

    0

    0

    1

    Malpighiales?

    Chontrocarpus (Leng et al. 2005)

    fruits

    0

    0

    0

    1

    Rosales

    Coahuilanthus belindae (Calvillo-Canadell and Cevallos-Ferriz 2007)

    flowers

    0

    0

    0

    1

    Fagales

    Dahlgrenianthus (Friis et al. 2006)

    flowers

    0

    0

    0

    3

    Rosales?

    Divisestylus (Hermsen et al. 2003)

    flowers and fruits

    0

    0

    0

    2

    Fagales

    Endressianthus (Friis et al. 2003)

    staminate inflorescences

    0

    0

    0

    1

    Assignment in Doubt

    Gassonoxylon araliosum (Wheeler and Lehman 2000)

    wood

    0

    0

    0

    1

    Malpighiales

    Lusicarpus planatus (Pedersen et al. 2007)

    pistillate flowers

    0

    0

    1

    0

    Malpighiales

    Lusistemon striatus (Pedersen et al. 2007)

    staminate flower

    0

    0

    1

    0

    Malpighiales?

    Maiandrocarpus (Leng et al. 2005)

    fruits

    0

    0

    0

    1

    Malpighiales?

    Malliocarpus (Leng et al. 2005)

    fruits

    0

    0

    0

    1

    Fagales

    Manningia (Friis 1983, Knobloch and Mai 1986, Friis and Crane 1989)

    flowers and fruits

    0

    0

    0

    1

    Malpighiales?

    Mitocarpus (Leng et al. 2005)

    fruits

    0

    0

    0

    1

    Malpighiales

    Paleoclusia chevalieri (Crepet and Nixon 1998)

    flowers and fruits

    0

    0

    1

    0

    Fagales

    Paraalnipollenites (X.-J. Sun et al. 1979)

    palynomorphs

    0

    0

    0

    1

    Rosales

    Platydiscus peltatus (Schönenberger et al. 2001)

    flower

    0

    0

    0

    1

    Fagales

    Protofagacea allonensis (Herendeen et al. 1995, Sims et al. 1998)

    flowers and inflorescences

    0

    0

    0

    1

    Assignment in Doubt

    Raoanthus intertrappea (Chitaley and Patel 1975)

    flowers and fruits

    0

    0

    0

    1

    Assignment in Doubt

    Silucarpus camptostylus (Pedersen et al. 2007)

    pistillate floral fragments

    0

    0

    1

    0

    Malpighiales

    Spanomera (Drinnan et al. 1991)

    inflorescence, staminate flowers, detached carpels and stamens

    0

    0

    2

    0

    Rosales?

    Tropidogyne pikei (Chambers et al. 2010)

    flower

    0

    0

    1

    0

    Assignment in Doubt

    Tylerianthus crossmanensis (Gandolfo et al. 1998)

    flowers and fruits

    0

    0

    1

    0

    Assignment in Doubt

    Valecarpus petiolatus (Pedersen et al. 2007)

    pistillate floral fragments

    0

    0

    1

    0

    Rosales

    Weinmannioxylon petriella (Poole et al. 2000)

    wood

    0

    0

    0

    1

    Malpighiales?

    Xylocarpus (Leng et al. 2005)

    fruits

    0

    0

    0

    1

    Malpighiales?

    Zeugarocarpus (Leng et al. 2005)

    fruits

    0

    0

    0

    1


    Asteranae. Asterids consists of several campanulid and lamiid orders, and at least five unplaced families (Chase and Reveal 2009). A South American origin of the largest family of asterids (Asteraceae) is suggested by extraordinary fossil finds of preserved capitulae and pollen in Eocene sediments of Patagonia (Barreda et al. 2010).

    The fossil history of asterids is reviewed in a paper by Martínez-Míllan (2010), who concludes that the group may be traced to the late Cretaceous at least 89 MYA. Asterid roots, at least based on lamid pollen records referable to Acanthaceae, may be traced to even older Mesozoic rocks (Tripp and McDade 2014).

    The photograph on the right-hand side of the page is Castilleja cinerea (Orobanchaceae, Lamiales, Asteranae) from the San Bernardino Mountains of southwestern North America.

    Kåre Bremer et al. (2004) also present evidence on the Cretaceous radiation of asterids. With the recent find of Burmese amber containing a preserved flower assignable to Cornaceae (Poinar et al. 2007), the fossil history of the group is indisputably older, at least to the Gallic Epoch (Albian Age) of the early Cretaceous Period.

    It is possible that the roots of asterids might lead deep into the Cretaceous stratigraphic record of yet undiscovered woody ancestors resembling modern Acanthaceae or Rubiaceae such as Guettarda and Psychotria (A. C. Smith and S. P. Darwin 1988).

    Origin of crown group Cornales in the Middle Cretaceous is inferred from molecular phylogenies calibrated by fossils (Xiang et al. 2011). Roots of Alangiaceae may be traced back to the upper Cretaceous (Feng et al. 2009).

    Having more than 13,000 species the Rubiaceae is among the largest families of flowering plants (Cronquist 1981). The fossil history of the family is reviewed by A. Graham (2009) and Martínez-Míllan (2010), among others.

    Leaves of certain rubiads are indistinguishable from Permian gigantopterids in details of cuticles, leaf midrib and petiole anatomy, and venation.

    Molecular phylogenetic studies of cpDNA sequences of the Lamiales shed new light on recent evolution of the group (Schäferhoff et al. 2010). Asteranae continue to be excellent research subjects for ecological and phylogenetic studies of shifting pollinators and the flowers they exploit (P. Wilson et al. 2007, S. D. Smith et al. 2008).

    Review papers and other key evo-devo and phylogenetic studies on asterids, Rubiaceae, and the Ericales clade have been published by Donoghue et al. (1998), Ree and Donoghue (1999), Anderberg et al. (2002), B. Bremer et al. (2002), Schönenberger et al. (2005), B. Bremer (2009), B. Bremer and Eriksson (2009), Howarth and Donoghue (2009), Reardon et al. (2009), and Viaene et al. (2009), among others.

    While work by C.-M. Feng et al. (2011) does not address higher level relationships among asterids, this paper opens a window toward deciphering morphological transitions from combined evo-devo and phylogenetic research perspectives.

    For example, recent gene expression studies of CYC-like genes among genera of plantagos suggest that duplication events in the lineage leading to Plantago caused disintegration of bilateral floral symmetry tool kits resulting in flowers adapted for wind pollination (Preston et al. 2011).

    Table 13 is the Mesozoic fossil history of asterids.


    Table 13. Mesozoic Stratigraphic Distribution of Asterids.

    Order

    Scientific Name and Publication

    Fossilized Remains

    Malm - Jurassic

    Neocomian - Cretaceous

    Gallic - Cretaceous

    Senonian - Cretaceous

    Assignment in Doubt

    undescribed (Friis et al. 2006)

    flower

    0

    0

    0

    1

    Cornales

    mastixiod fruits (Knobloch and Mai 1986)

    fruits

    0

    0

    0

    >2?

    Ericales

    Actinocalyx bohrii (Friis 1985)

    flowers, fruits, seeds

    0

    0

    0

    1

    Cornales

    Eoepigynia burmensis (Poinar et al. 2007)

    flower

    0

    0

    1

    0

    Ericales

    Eurya (Knobloch and Mai 1986)

    fruits and seeds

    0

    0

    0

    1?

    Cornales

    Hironoia fusiformis (Takahashi et al. 2003)

    flowers

    0

    0

    0

    1

    Ericales

    Leucothoe (Knobloch and Mai 1986)

    fruits and seeds

    0

    0

    0

    1?

    Ericales

    Paleoenkianthus sayrevillensis (Nixon and Crepet 1993)

    flowers and fruits

    0

    0

    1

    0

    Ericales

    Paradinandra suecica (Schönenberger and Friis 2001)

    flowers

    0

    0

    0

    1

    Ericales

    Parasaurauia allonensis (Keller et al. 1996)

    flowers and fruits

    0

    0

    1

    0

    Ericales

    Pentapetalum trifasciculandricus (Martínez-Míllan et al. 2009)

    flowers

    0

    0

    1

    0

    Ericales

    Saurauia (Knobloch and Mai 1986)

    fruits and seeds

    0

    0

    0

    1?

    Assignment in Doubt

    Scandianthus costatus (Friis and Skarby 1982)

    flowers and fruits

    0

    0

    0

    1


    There are two papers dealing with recovery of angiosperm and phytophagous insect clades and European and Neotropical forests following the Chicxulub bolide impact and ensuing K-Pg mass extinction (Wappler et al. 2009 and Wing et al. 2009).

    Studies of the decline of tropical floras following the Oligocene-Eocene climatic cooling, "escape and radiation" coevolution (Winkler et al. 2009), phytophagy (Winkler et al. 2010), basal angiosperm phylogeography (Luna-Vega and Magallón 2010), and the spread and shrinking of Arctic floras during the pluvials, serve as gateways to the vast literature on Cenozoic paleoclimatology, paleontology, and coevolving clades of flowering plants and Holometabola.

    The most comprehensive work on Mesozoic and Cenozoic fossil angiosperms to date is T. N. Taylor et al. (Chapter 22, 2009). A review of the fossil history, evolution, and cladogenesis of flowering plants of the Paleogene and Neogene Period is beyond the scope of the present essay.


    Conclusions on the Evolution of Mesozoic Angiosperms:

    There are great gaps in our understanding of the fossil history of flowering plants based on data recorded in Tables 7-13 and detailed case-bound reviews by T. N. Taylor et al. (2009) and Friis et al. (2011). Paleontologic data reveal several general trends but due to insufficient sampling it is too soon to make any definitive statements on the origin, paleobiodiversity, and evolution of angiosperms. Deciphering the genomic landscape of Amborella trichopoda, albeit an accomplished scientific effort, is probably unhelpful in understanding allopolyploidy in long-extinct populations of stem-group flowering plants, solving origins of angiosperms, or disentangling evolution of GRNs of protoflowers.

    Arber, Leppik, and Parkin's classical proposals on protoflowers were probably correct but remain untested by evolutionary-developmental studies of the molecular tool kit. Concomitantly, fossil evidence of ancient angiosperm flowers and protoflowers has yet to be mined from the rocks or pieced together from detached and shed foliar organs. Further, DNA-binding foliar and floral tool kit proteins, specifically Class III HD-Zip, KNOTTED, LEAFY, and WUSCHEL, are deeply conserved.

    From an evo-devo research perspective the angiosperm flower is a deeply conserved seed plant structure, which is essentially a reproductive short- [spur-] shoot (Christianson and Jernstedt 2009). Consequently, Chanderbali et al. (2016) forgot to discuss an earlier study published on page 2635 of The EMBO Journal (Hamès et al. 2008, which stated "... the acquisition of R390 [amino acid residue 390 of LEAFY protein] might therefore have been important for flower evolution ..." (the phrase in brackets [] is mine).

    Paleobotanical data in the preceding tables often consist of a single specimen from one isolated locality (sometimes only a single, tiny charcoalified flower or seed), and therefore, can no way support assertions of a "Big Bang," "explosive," or "first" radiation of angiosperms in early Cretaceous paleoenvironments. Considerably more field work is needed with possible focus on outcrops older in geologic age.

    In view of the discovery of the Barremian (Neocomian) eudicot Leefructus (G. Sun et al. 2011) and other fossil discoveries, I predict that magnoliid, monocot and eudicot fossils will eventually be found in Tithonian (Malm) rocks. Certain paleobotanists impede progress in understanding stem-group flowering plants by not citing or discussing published work reporting several occurrences of Afropollis and Sanmiguelia from Triassic (Anisian and Norian) core samples and rock outcrops. By leaving out critical, stratigraphically-controlled angiosperm guide fossils in calibrated molecular phylogenies, some workers invalidate dated clade-divergences and cloud tree-thinking.

    Coevolution between phytophagous insect antagonists and Carboniferous, Permian, and Triassic seed plant hosts at the level of their respective developmental tool kits and CRMs was likely. I completely reject the notion of a Cretaceous origin of flowering plants. My opinion is supported by molecular phylogenetic analysis of nucleic acid data suggesting a late Triassic (Norian) age of the flowering plant crown group (Stephen A. Smith et al. 2010). Hochuli and Feist-Burkhardt palynological studies (2013) that report monosulcate, columellate palynomorphs, and Afropollis from the Middle Triassic (Anisian) about 240 MYA, are unequivocal.

    Potential reticulations in paraphyletic lines of gymnosperms existing at the time of the divergence of angiosperms from the MRCA bracketed by molecular clock studies (Magállon 2010) might be associated with ancient swarms of seed plant WGDs modeled by Jiao et al. (2011) occurring prior to the end-Permian extinction. Later phylogenies by Magállon (2015) are not calibrated with Sanmiguelia lewisii, which is probably a basal monocotyledonous flowering plant.

    Genomic studies of the cultivated grape overwhelmingly support paleohexaploidy (Jaillon et al. 2007), which is equivalent to the "γ [gamma] triplication" cited by Jiao et al. (2011, the word in brackets[] is mine) that occurred in the common ancestor of eudicots and monocots. A pivotal study of the Nelumbo nucifera genome (Yun Wang et al. 2013), which is strangely overlooked by P. S. Soltis and D. E. Soltis (2016), reveals absence of the γ triplication in this basalmost eudicot species. A later-diverging clade of Gunnerales exhibits paleohexaploidy.

    Adaptive radiation within the major clades of eudicots, rosids, and asterids during the Cretaceous Period is evident from paleontological data summarized by Crepet et al. (2004), Friis et al. (2006), D. E. Soltis et al. (2008), T. N. Taylor et al. (2009), and Friis et al. (2011). Positioning Ceratophyllales in relation to Nelumbo nucifera by the Angiosperm Phylogeny Group to include genomic studies of Ceratophyllum demersum, is probably important.

    Clues from our redoubled efforts to excavate ("mining the rock record") and to painstakingly study coalified, compressed, permineralized, petrified, and preserved fossil plant material (page 249, E. L. Taylor and T. N. Taylor 2009), to better understand the anatomy, biology, and morphology of coevolving colonies of holometabolous insect antagonists, and to reconstruct whole protoflowers, might help us solve the riddle of angiosperm beginnings within an evolutionary framework.

    The Cretaceous Period is better regarded as a late Mesozoic link between earlier paleofloras and faunas of the Jurassic, Triassic, Permian, and Carboniferous periods, and later insect-plant compartments of the Tertiary (Paleogene and Neogene periods) and Quaternary intervals of the Cenozoic Era. A Paleozoic origin of angiosperms is possible based on convincing evidence in the literature that points to deep conservation of floral tool kits. Future tool kit phylogenies should be calibrated with fossils.

    A concerted effort by paleobotanists is needed to identify the putative 160 million year old angiosperm ghost lineage by unearthing, studying, and describing more fossil flowers and fruits from older Cretaceous, Jurassic, and Triassic beds, to include basic paleobotanical surveys of earlier Paleozoic sedimentary deposits. I conclude that insect-mediated intergeneric natural hybridization among populations of Paleozoic gigantopteroids and possibly Vojnovskyales, followed by spontaneous paleopolyploidy and dispersal of hybrid offspring, spread molecular tool kit novelties in ancestral early Triassic ghost lineages of angiosperms, including ceratophyllaleans, magnoliids, and sanmiguelias that survived the PTr.

    Seemingly intractable questions in seed plant evolution may be answered through collaborative, interdisciplinary research studies by biochemists, developmental biologists, entomologists, molecular systematists, and paleobotanists. Progress in understanding at least some aspects of the enigmatic origin of angiosperms is no longer a futile exercise. Mesozoic times should no longer be the only focus of our quest to solve the riddle of flowering plant evolution. Studies of the Amborella trichopoda genome do not offer a solution to the origin of angiosperms. The origin(s) of flowering plants and the angiosperm flower might never be fully understood.


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    ESSAY CONTENTS

  • Angiosperm Classification
  • Angiosperm Ghost Lineage
  • Basal Angiosperms
  • Commelinid Monocots
  • Conclusions on the Evolution of Mesozoic Angiosperms
  • Core Eudicots, Rosids, and Asterids
  • Cretaceous Explosive Radiation of Angiosperms
  • Crown Group Flowering Plants
  • Eudicots
  • Fossil History
  • Literature Cited on the Evolution of Mesozoic Angiosperms
  • Monocots
  • Stem Group Flowering Plants

  • AUGUST 1, 2016


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