Origin and Evolution of Flowering Plants

Essays on the Origin of Angiosperms

One route toward understanding flowering-plant origins is to examine how developmental tool kits, cis-regulatory modules (CRMs) and gene-regulatory networks (GRNs) changed across ancient seed-plant lineages. Coevolution with insects may have helped shape reproductive short shoots and structures that can be discussed as possible protoflower precursors. Evo-devo research provides one framework for testing these ideas.

Late Paleozoic seed-plant shrubs occupied environments shared with diverse insects. Those ecological associations invite questions about whether pollinivory, herbivory and other interactions contributed to the evolution of reproductive organs. The broader hypothesis is explored in Origin of Angiosperms.

Hybridization and allopolyploidy may also have been significant in ancient seed-plant populations. Rather than treating pteridosperms as a simple evolutionary backbone, the fossil record can be approached as a network of lineages whose relationships may have included reticulation. See Paleobotany of Angiosperm Origins.

Genomic work on Amborella trichopoda is valuable for living angiosperm biology, but by itself cannot reconstruct Permian populations, zones of sympatry or ancient hybridization. Fossils, morphology, developmental genetics and stratigraphy therefore have to be considered together. See Evolution of Flowering Plants.

Fluctuating Paleozoic oxygen levels formed the environmental background for insects that chewed, pierced, sucked, crawled and oviposited on seed plants. Reproductive foliar organs arranged around short shoots could have participated in these ecological systems, potentially combining visual, structural and nutritional functions.

The long-standing difficulty remains the same one associated with Darwin's “abominable mystery”: how and when did the flower and flowering plants arise? Modern genomic evidence has expanded the problem rather than eliminating the need to reconcile developmental hypotheses with fossils.

Climate is another part of the context. Poulsen, Tabor and White (2015) discussed long-term climate forcing linked with atmospheric oxygen concentration, while paleobiological interpretations must also account for precipitation, sedimentation and changing habitats through deep time.

Sheltered spaces among leathery leaves, developing stems and reproductive modules may have offered phytophagous insects food, refuge and localized air spaces. Such ecological details matter when reconstructing how ancient seed plants and their insect associates interacted.

Debate, Literature and Research News

The site's research-news material connects discussions of flowering-plant origins with work on Holometabola and related subjects, combining scientific literature with commentary and illustrations. Continue to Research News or the Topics for Debate and Discussion.

For advanced biology students, the Charles Darwin Bicentennial Reading List organizes books and chapters useful for deeper study. The literature guide is continued in the Key to the Literature.

The site's “Publication of the Year” feature highlights papers, chapters or books considered especially useful for investigating the unresolved evolutionary history of flowering plants and their interactions with holometabolous insects. Read more.

Problems for Students of Paleobiology

Fossil biometry, heterochrony, morphospace, paleobiogeography, paleoecology and phylogenetics all provide testable research problems. Graduate students and postdoctoral researchers can investigate taphonomy of detached reproductive organs and use quantitative morphology to reconstruct cones and flowers. Reconstructing Cones and Flowers.

Practice material includes a seed-plant homology assessment and a sample data matrix for morphological phylogenetic analysis.

Palynological records from ancient sediments can be used as exercises in calibrating pollen trees, while fossil reproductive shoots raise ecological questions about attraction or deterrence of pollinivores, paleodictyopterans and predatory wasps. See Calibrating Pollen Trees and 3-D Floral Constructs.

GIS, georeferencing and paleomapping can further help reconstruct ancient distributions and possible zones of hybridization. Vicariance Paleobiogeography.

The Clear Fork Gigantopteroid

Clear Fork Group sediments accumulated in riverine oxbows along Artinskian–Cisuralian coastlines more than 256 million years ago. Their geological setting is relevant to reconstructions of the Central Pangaean Mountains and Hovey Channel.

Leaves identified as Evolsonia texana and a retuse-leaved Taeniopteris morphotype occur together in particular Clear Fork red-bed layers. Their association raises the possibility that these herbivorized organs belonged to short and long shoots of a gigantopteroid seed plant rather than to the better-known groups with which similar foliage has sometimes been compared.

Vojnovskyales and gigantopteroids remain incompletely understood Permo-Carboniferous gymnosperms. Some authors have discussed possible evolutionary connections with flowering plants or Gnetum, making anatomical study of fossils especially important.

Permineralized material of Delnortea abbottiae, Evolsonia texana and Zeilleropteris wattii, combined with theoretical morphospace, may clarify how these plants relate to other seed plants. Delnorteas, Evolsonias and Other Gigantopteroids.

The foliage of Vojnovskyales has also been compared with the Triassic monocot-like plant Sanmiguelia. These morphological parallels provide additional questions for research into developmental patterns of ancient seed plants. See Vojnovskyales and Sanmiguelias.

Evolution of Flowering Plants

The Amborella trichopoda genome cannot, on its own, resolve the origin of angiosperms. Its greater value may lie in showing how gene-regulatory and auxin-polarity networks were reorganized through evolution. When ancient hybridization and allopolyploidy are added to an incomplete fossil record, flowering-plant origins remain a difficult historical problem.

If fertile reproductive short shoots are securely documented in late Paleozoic seed plants, their existence must be considered when evaluating models that place the origin of flowers much later. Chanderbali and colleagues (2016) revisited this broader paradox in the genomic era.

Biophysical studies of homeodomain proteins, transcription factors, CRMs, GRNs and auxin-based polarity networks point to deeply conserved developmental machinery. This makes it useful to compare molecular mechanisms with the anatomy and morphology of reproductive short shoots.

Structural work on LEAFY and related regulatory systems adds another layer to hypotheses about the floral developmental switch. See LEAFY Enzyme Structure.

Whole-genome duplications have likewise been proposed as sources of genetic material for major angiosperm innovations. Their timing and interpretation remain relevant to discussions of protoflowers and early floral evolution. WGDs.

Fossil pollen, including angiosperm-like palynomorphs and Afropollis, must be assessed alongside molecular phylogenies and stratigraphy. The tension between molecular divergence estimates and the fossil record is central to the proposed angiosperm ghost lineage.

Developmental models based on CRMs, GRNs and PINs can also be used to explore angio-ovuly and reproductive morphology in fossil seed plants. Quantitative reconstructions in theoretical morphospace provide a way to test proposed Permian protoflowers.

Transposable elements, including LTR retrotransposons, are another possible component of genome evolution that deserves consideration in models of flowering-plant origins. LTR Retrotransposons.

Paleoclimate proxies derived from stomata, wood and carbon isotopes are used to estimate atmospheric conditions over hundreds of millions of years. Their uncertainties matter when linking genome evolution, polyploidy and ecological change. Paleopolyploidy, Proxies and Global Hot Houses.

Plant–insect interactions may also have involved chemical and mechanical signals affecting developing meristems. This possibility is explored as a hypothesis rather than an established mechanism. Signals.

Episodes of acidification, hypoxia and warming shaped terrestrial ecosystems around major extinction intervals. Evidence from the Karoo Basin has been used to question simple narratives that synchronize aridification, floral collapse and tetrapod turnover. Paleoecology of Global Catastrophe.

Biostratigraphy of a Permian Standard Section

Folded and overthrust mountain belts in southwestern North America expose an unusually complete succession of Paleozoic rocks. A bedding sequence in the Del Norte and Glass Mountains serves as a standard North American type section for the Permian Period.

These rocks preserve fossil reef communities with brachiopods, conodonts, fusulinids, graptolites and sponges, together with transitional deltaic layers containing freshwater snails, walchian conifers and gigantopteroid seed plants. Read the article.

Living “Fossil” Magnoliids: Degeneriaceae of Fiji

South Pacific island floras include lineages with strong biogeographic interest. Degeneriaceae consists of one genus and two species of magnoliid timber trees endemic to the Fijian islands of Taveuni, Vanua Levu and Viti Levu.

Molecular phylogenetic research on magnoliids has revealed relationships between Degeneria roseiflora and other members of the group that are useful for interpreting character evolution.

Degenerias combine several notable angiosperm traits, including carpels with stigmatic secretions, laminar microsporophylls, monosulcate pollen, polycotyledony and very small embryos. Notes from the Field.

Statement on Evolution

The site owner, writer, peer reviewers and contributors identify their approach with the Botanical Society of America's policy on evolution.