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Klymiuk AA, Rothwell GW, Stockey RA. A novel cupulate seed plant, Xadzigacalix quatsinoensis gen. et sp. nov., provides new insight into the Mesozoic radiation of gymnosperms. AMERICAN JOURNAL OF BOTANY 2022; 109:966-985. [PMID: 35435244 PMCID: PMC9328379 DOI: 10.1002/ajb2.1853] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/16/2021] [Revised: 04/14/2022] [Accepted: 04/15/2022] [Indexed: 06/14/2023]
Abstract
PREMISE Anatomically preserved evidence for a novel clade of gymnosperms emphasizes diversity of seed plants immediately prior to the appearance of angiosperm fossils in the paleontological record. METHODS Cupulate seeds from the Early Cretaceous Apple Bay locality (Vancouver Island) are described from serial cellulose acetate peels and three-dimensional reconstruction. Phylogenetic context is assessed through the comparative analysis of gymnosperm seed producing fructifications and maximum parsimony analysis of a revised morphological data set for seed plant phylogeny. RESULTS Xadzigacalix quatsinoensis gen. et sp. nov. is characterized by an orthotropous ovule with an elongated micropyle and complex integument, enclosed within a radial cupule. The micropylar canal is elongated; and the nucellus extends into the micropyle to seal the post pollination ovule. Except at the apex of the micropyle, the seed is completely enclosed by a parenchymatous cupule with ca. 20 axially elongated secretory ducts. The cupulate seed is produced upon a triangular woody stele, consisting of a parenchymatous pith surrounded by radially aligned tracheids. The stele produces three short terete traces that terminate within the base of the cupule as transfusion tissue at the seed chalaza. CONCLUSIONS Organography, vascularization, nature of the integument and nucellus, and configuration of the micropylar canal distinguish Xadzigacalix quatsinoensis from all other gymnosperm clades. Cladistic analyses suggest the new plant may have affinities with gnetophytes or angiosperms. These results are complemented with a critical re-evaluation of ovulate structures for Mesozoic gymnosperms, providing new insight into plant diversity immediately antecedent to the explosive diversification of flowering plants.
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Affiliation(s)
- Ashley A. Klymiuk
- Department of Biological SciencesUniversity of ManitobaWinnipegManitobaR3T 2N2Canada
- Gantz Family Collections Center, Field Museum, 1400 S Lake Shore DriveChicagoIL60605USA
| | - Gar W. Rothwell
- Department of Botany and Plant PathologyOregon State UniversityCorvallisOR97331−2902USA
- Department of Environmental and Plant Biology317 Porter Hall, Ohio UniversityAthensOH45701USA
| | - Ruth A. Stockey
- Department of Botany and Plant PathologyOregon State UniversityCorvallisOR97331−2902USA
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2
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Shi G, Herrera F, Herendeen PS, Clark EG, Crane PR. Mesozoic cupules and the origin of the angiosperm second integument. Nature 2021; 594:223-226. [PMID: 34040260 DOI: 10.1038/s41586-021-03598-w] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2020] [Accepted: 04/30/2021] [Indexed: 11/09/2022]
Abstract
The second integument of the angiosperm ovule is unique among seed plants, with developmental genetics that are distinct from those of the inner integument1. Understanding how the second integument should be compared to structures in other seed plants is therefore crucial to resolving the long-standing question of the origin of angiosperms2-6. Attention has focused on several extinct plants with recurved cupules that are reminiscent of the anatropous organization of the basic bitegmic ovules of angiosperms1-6, but interpretations have been hampered by inadequate information on the relevant fossils. Here we describe abundant exceptionally well-preserved recurved cupules from a newly discovered silicified peat dating to the Early Cretaceous epoch (around 125.6 million years ago) in Inner Mongolia, China. The new material, combined with re-examination of potentially related fossils, indicates that the recurved cupules of several groups of Mesozoic plants are all fundamentally comparable, and that their structure is consistent with the recurved form and development of the second integument in the bitegmic anatropous ovules of angiosperms. Recognition of these angiosperm relatives (angiophytes) provides a partial answer to the question of angiosperm origins, will help to focus future work on seed plant phylogenetics and has important implications for ideas on the origin of the angiosperm carpel.
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Affiliation(s)
- Gongle Shi
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing, China.
| | | | | | | | - Peter R Crane
- Oak Spring Garden Foundation, Upperville, VA, USA.,Yale School of the Environment, Yale University, New Haven, CT, USA
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3
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Gasser CS, Skinner DJ. Development and evolution of the unique ovules of flowering plants. Curr Top Dev Biol 2018; 131:373-399. [PMID: 30612624 DOI: 10.1016/bs.ctdb.2018.10.007] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Ovules are the precursors to seeds and as such are critical to plant propagation and food production. Mutant studies have led to the identification of numerous genes regulating ovule development. Genes encoding transcription factors have been shown to direct ovule spacing, ovule identity and integument formation. Particular co-regulators have now been associated with activities of some of these transcription factors, and other protein families including cell surface receptors have been shown to regulate ovule development. Hormone levels and transport, especially of auxin, have also been shown to play critical roles in ovule emergence and morphogenesis and to interact with the transcriptional regulators. Ovule diversification has been studied using orthologs of regulatory genes in divergent angiosperm groups. Combining modern genetic evidence with expanding knowledge of the fossil record illuminates the possible origin of the unique bitegmic ovules of angiosperms.
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Affiliation(s)
- Charles S Gasser
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA, United States.
| | - Debra J Skinner
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA, United States
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4
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Spencer ART, Garwood RJ, Rees AR, Raine RJ, Rothwell GW, Hollingworth NTJ, Hilton J. New insights into Mesozoic cycad evolution: an exploration of anatomically preserved Cycadaceae seeds from the Jurassic Oxford Clay biota. PeerJ 2017; 5:e3723. [PMID: 28875075 PMCID: PMC5578371 DOI: 10.7717/peerj.3723] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2017] [Accepted: 07/31/2017] [Indexed: 11/20/2022] Open
Abstract
Most knowledge concerning Mesozoic Era floras has come from compression fossils. This has been augmented in the last 20 years by rarer permineralized material showing cellular preservation. Here, we describe a new genus of anatomically preserved gymnosperm seed from the Callovian-Oxfordian (Jurassic) Oxford Clay Formation (UK), using a combination of traditional sectioning and synchrotron radiation X-ray micro-tomography (SRXMT). Oxfordiana motturii gen. et sp. nov. is large and bilaterally symmetrical. It has prominent external ribs, and has a three-layered integument comprising: a narrow outer layer of thick walled cells; a thick middle parenchymatous layer; and innermost a thin fleshy layer. The integument has a longitudinal interior groove and micropyle, enveloping a nucellus with a small pollen chamber. The large size, bilateral symmetry and integumentary groove demonstrate an affinity for the new species within the cycads. Moreover, the internal groove in extant taxa is an autapomorphy of the genus Cycas, where it facilitates seed germination. Based upon the unique seed germination mechanism shared with living species of the Cycadaceae, we conclude that O. motturii is a member of the stem-group lineage leading to Cycas after the Jurassic divergence of the Cycadaceae from other extant cycads. SRXMT-for the first time successfully applied to fossils already prepared as slides-reveals the distribution of different mineral phases within the fossil, and allows us to evaluate the taphonomy of Oxfordiana. An early pyrite phase replicates the external surfaces of individual cells, a later carbonate component infilling void spaces. The resulting taphonomic model suggests that the relatively small size of the fossils was key to their exceptional preservation, concentrating sulfate-reducing bacteria in a locally closed microenvironment and thus facilitating soft-tissue permineralization.
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Affiliation(s)
- Alan R T Spencer
- Department of Earth Science and Engineering, Imperial College London, London, UK
| | - Russell J Garwood
- School of Earth and Environmental Sciences, University of Manchester, Manchester, UK.,Department of Earth Sciences, The Natural History Museum London, London, UK
| | - Andrew R Rees
- School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK
| | | | - Gar W Rothwell
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR, USA.,Department of Environmental and Plant Biology, Ohio University, Athens, OH, USA
| | - Neville T J Hollingworth
- School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK.,Science and Technology Facilities Council, Swindon, UK
| | - Jason Hilton
- School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK.,Birmingham Institute of Forest Research, University of Birmingham, Birmingham, UK
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5
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Liu ZJ, Wang X. Yuhania: a unique angiosperm from the Middle Jurassic of Inner Mongolia, China. HISTORICAL BIOLOGY 2017; 29:431-441. [PMID: 28392623 PMCID: PMC5359780 DOI: 10.1080/08912963.2016.1178740] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2016] [Accepted: 04/12/2016] [Indexed: 05/10/2023]
Abstract
Despite increasing claims of pre-Cretaceous angiosperms, whether there really are angiosperms in the Jurassic is apparently still an open question for many people before further evidence is available. This question can only be answered by studying more Jurassic plant fossils. Here we report a fossil angiosperm, Yuhania daohugouensis gen. et sp. nov, from the Middle Jurassic of Inner Mongolia, China. The plant includes connected stem, leaves, flowers, aggregate fruits, fruitlets, and seeds within fruitlets. The leaves are helically arranged along the curving stem, linear in shape, with 5-6 parallel veins. The aggregate fruit is pedicellate, composed of over 20 carpels/fruitlets helically arranged. Each fruitlet encloses a seed. The reproductive organs in various stages are found in the same plant, allowing us to understand the development of Yuhania. The occurrence of Yuhania in the Middle Jurassic re-confirms the Jurassic history for angiosperms that has been suggested by other independent research and adds to the on-going study on the early evolution of angiosperms.
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Affiliation(s)
- Zhong-Jian Liu
- Shenzhen Key Laboratory for Orchid Conservation and Utilization, National Orchid Conservation Center of China and Orchid Conservation & Research Center of Shenzhen, Shenzhen518114, China
| | - Xin Wang
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, CAS, Nanjing210008, China
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6
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Herrera F, Shi G, Ichinnorov N, Takahashi M, Bugdaeva EV, Herendeen PS, Crane PR. The presumed ginkgophyte Umaltolepis has seed-bearing structures resembling those of Peltaspermales and Umkomasiales. Proc Natl Acad Sci U S A 2017; 114:E2385-E2391. [PMID: 28265050 PMCID: PMC5373332 DOI: 10.1073/pnas.1621409114] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The origins of the five groups of living seed plants, including the single relictual species Ginkgo biloba, are poorly understood, in large part because of very imperfect knowledge of extinct seed plant diversity. Here we describe well-preserved material from the Early Cretaceous of Mongolia of the previously enigmatic Mesozoic seed plant reproductive structure Umaltolepis, which has been presumed to be a ginkgophyte. Abundant new material shows that Umaltolepis is a seed-bearing cupule that was borne on a stalk at the tip of a short shoot. Each cupule is umbrella-like with a central column that bears a thick, resinous, four-lobed outer covering, which opens from below. Four, pendulous, winged seeds are attached to the upper part of the column and are enclosed by the cupule. Evidence from morphology, anatomy, and field association suggests that the short shoots bore simple, elongate Pseudotorellia leaves that have similar venation and resin ducts to leaves of living GinkgoUmaltolepis seed-bearing structures are very different from those of Ginkgo but very similar to fossils described previously as Vladimaria. Umaltolepis and Vladimaria do not closely resemble the seed-bearing structures of any living or extinct plant, but are comparable in some respects to those of certain Peltaspermales and Umkomasiales (corystosperms). Vegetative similarities of the Umaltolepis plant to Ginkgo, and reproductive similarities to extinct peltasperms and corystosperms, support previous ideas that Ginkgo may be the last survivor of a once highly diverse group of extinct plants, several of which exhibited various degrees of ovule enclosure.
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Affiliation(s)
| | - Gongle Shi
- Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, People's Republic of China
| | - Niiden Ichinnorov
- Institute of Paleontology and Geology, Mongolian Academy of Sciences, Ulaanbaatar-51, Mongolia
| | - Masamichi Takahashi
- Department of Environmental Sciences, Faculty of Sciences, Niigata University, Ikarashi, Nishi-ku, Niigata 950-2181, Japan
| | - Eugenia V Bugdaeva
- Institute of Biology and Soil Science, Far East Branch, Russian Academy of Sciences, Vladivostok 690022, Russia
| | | | - Peter R Crane
- School of Forestry and Environmental Studies, Yale University, New Haven, CT 06511;
- Oak Spring Garden Foundation, Oak Spring, Upperville, VA 20184
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7
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Shi G, Leslie AB, Herendeen PS, Herrera F, Ichinnorov N, Takahashi M, Knopf P, Crane PR. Early Cretaceous Umkomasia from Mongolia: implications for homology of corystosperm cupules. THE NEW PHYTOLOGIST 2016; 210:1418-29. [PMID: 26840646 DOI: 10.1111/nph.13871] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2015] [Accepted: 12/17/2015] [Indexed: 05/21/2023]
Abstract
Corystosperms, a key extinct group of Late Permian to Early Cretaceous plants, are important for understanding seed plant phylogeny, including the evolution of the angiosperm carpel and anatropous bitegmic ovule. Here, we describe a new species of corystosperm seed-bearing organ, Umkomasia mongolica sp. nov., based on hundreds of three-dimensionally preserved mesofossils from the Early Cretaceous of Mongolia. Individual seed-bearing units of U. mongolica consist of a bract subtending an axis that bifurcates, with each fork (cupule stalk) bearing a cupule near the tip. Each cupule is formed by the strongly reflexed cupule stalk and two lateral flaps that partially enclose an erect seed. The seed is borne at, or close to, the tip of the reflexed cupule stalk, with the micropyle oriented towards the stalk base. The corystosperm cupule is generally interpreted as a modified leaf that bears a seed on its abaxial surface. However, U. mongolica suggests that an earlier interpretation, in which the seed is borne directly on an axis (shoot), is equally likely. The 'axial' interpretation suggests a possible relationship of corystosperms to Ginkgo. It also suggests that the cupules of corystosperms may be less distinct from those of Caytonia than has previously been supposed.
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Affiliation(s)
- Gongle Shi
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing, 210008, China
- School of Forestry and Environmental Studies, Yale University, 195 Prospect Street, New Haven, CT, 06511, USA
| | - Andrew B Leslie
- Department of Ecology and Evolutionary Biology, Brown University, Providence, RI, 02912, USA
| | | | - Fabiany Herrera
- Chicago Botanic Garden, 1000 Lake Cook Road, Glencoe, IL, 60022, USA
| | - Niiden Ichinnorov
- Paleontological Center, Mongolian Academy of Sciences, PO Box 260, Ulaanbaatar-51, Mongolia
| | - Masamichi Takahashi
- Department of Environmental Sciences, Faculty of Sciences, Niigata University, 8050, 2-cho, Ikarashi, Nishi-ku, Niigata, 950-2181, Japan
| | - Patrick Knopf
- Botanischer Garten Rombergpark, Am Rombergpark 49b, Dortmund, 44225, Germany
| | - Peter R Crane
- School of Forestry and Environmental Studies, Yale University, 195 Prospect Street, New Haven, CT, 06511, USA
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8
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Rothwell GW, Stockey RA. Phylogenetic diversification of Early Cretaceous seed plants: The compound seed cone of Doylea tetrahedrasperma. AMERICAN JOURNAL OF BOTANY 2016; 103:923-937. [PMID: 27208360 DOI: 10.3732/ajb.1600030] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2016] [Accepted: 03/07/2016] [Indexed: 06/05/2023]
Abstract
PREMISE OF THE STUDY Discovery of cupulate ovules of Doylea tetrahedrasperma within a compact, compound seed cone highlights the rich diversity of fructification morphologies, pollination biologies, postpollination enclosure of seeds, and systematic diversity of Early Cretaceous gymnosperms. METHODS Specimens were studied using the cellulose acetate peel technique, three-dimensional reconstructions (in AVIZO), and morphological phylogenetic analyses (in TNT). KEY RESULTS Doylea tetrahedrasperma has bract/fertile short shoot complexes helically arranged within a compact, compound seed cone. Complexes diverge from the axis as a single unit and separate distally into a free bract tip and two sporophylls. Each sporophyll bears a single, abaxial seed, recurved toward the cone axis, that is enveloped after pollinaton by sporophyll tissue, forming a closed cupule. Ovules are pollinated by bisaccate grains captured by micropylar pollination horns. CONCLUSIONS The unique combination of characters shown by D. tetrahedrasperma includes the presence of cupulate seeds borne in conifer-like compound seed cones, an ovuliferous scale analogue structurally equivalent to the ovulate stalk of Ginkgo biloba, gymnospermous pollination, and nearly complete enclosure of mature seeds. These features characterize the Doyleales ord. nov., clearly distinguish it from the seed fern order Corystospermales, and allow for recognition of another recently described Early Cretaceous seed plant as a second species in genus Doylea. A morphological phylogenetic analysis highlights systematic relationships of the Doyleales ord. nov. and emphasizes the explosive phylogenetic diversification of gymnosperms that was underway at the time when flowering plants may have originated and/or first began to radiate.
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Affiliation(s)
- Gar W Rothwell
- Department of Botany and Plant Pathology, 2082 Cordley Hall, Oregon State University, Corvallis, Oregon 97331, USA Department of Environmental and Plant Biology, Ohio University, Athens, Ohio 45701, USA
| | - Ruth A Stockey
- Department of Botany and Plant Pathology, 2082 Cordley Hall, Oregon State University, Corvallis, Oregon 97331, USA
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9
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Endress PK. Angiosperm ovules: diversity, development, evolution. ANNALS OF BOTANY 2011; 107:1465-89. [PMID: 21606056 PMCID: PMC3108811 DOI: 10.1093/aob/mcr120] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2011] [Revised: 03/29/2011] [Accepted: 04/11/2011] [Indexed: 05/18/2023]
Abstract
BACKGROUND Ovules as developmental precursors of seeds are organs of central importance in angiosperm flowers and can be traced back in evolution to the earliest seed plants. Angiosperm ovules are diverse in their position in the ovary, nucellus thickness, number and thickness of integuments, degree and direction of curvature, and histological differentiations. There is a large body of literature on this diversity, and various views on its evolution have been proposed over the course of time. Most recently evo-devo studies have been concentrated on molecular developmental genetics in ovules of model plants. SCOPE The present review provides a synthetic treatment of several aspects of the sporophytic part of ovule diversity, development and evolution, based on extensive research on the vast original literature and on experience from my own comparative studies in a broad range of angiosperm clades. CONCLUSIONS In angiosperms the presence of an outer integument appears to be instrumental for ovule curvature, as indicated from studies on ovule diversity through the major clades of angiosperms, molecular developmental genetics in model species, abnormal ovules in a broad range of angiosperms, and comparison with gymnosperms with curved ovules. Lobation of integuments is not an atavism indicating evolution from telomes, but simply a morphogenetic constraint from the necessity of closure of the micropyle. Ovule shape is partly dependent on locule architecture, which is especially indicated by the occurrence of orthotropous ovules. Some ovule features are even more conservative than earlier assumed and thus of special interest in angiosperm macrosystematics.
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Affiliation(s)
- Peter K Endress
- Institute of Systematic Botany, University of Zurich, Zollikerstrasse 107, 8008 Zurich, Switzerland.
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Leslie AB. Flotation preferentially selects saccate pollen during conifer pollination. THE NEW PHYTOLOGIST 2010; 188:273-9. [PMID: 20579290 DOI: 10.1111/j.1469-8137.2010.03356.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
• Among many species of living conifers the presence of pollen with air bladders (saccate pollen) is strongly associated with downward-facing ovules and the production of pollination drops. This combination of features enables saccate pollen grains captured in the pollination drop to float upwards into the ovule. Despite the importance of this mechanism in understanding reproduction in living conifers and in extinct seed plants with similar morphologies, experiments designed to test its effectiveness have yielded equivocal results. • In vitro and in vivo pollination experiments using saccate and nonsaccate pollen were performed using modeled ovules and two Pinus species during their natural pollination period. • Buoyant saccate pollen readily floated through aqueous droplets, separating these grains from nonbuoyant pollen and spores. Ovules that received saccate pollen, nonsaccate pollen or a mixture of both all showed larger amounts and higher proportions of saccate pollen inside ovules after drop secretion. • These results demonstrate that flotation is an effective mechanism of pollen capture and transport in gymnosperms, and suggest that the prevalence of saccate grains and downward-facing ovules in the evolutionary history of seed plants is a result of the widespread use of this mechanism.
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Affiliation(s)
- Andrew B Leslie
- Department of the Geophysical Sciences, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA.
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Stockey RA, Rothwell GW. Distinguishing angiophytes from the earliest angiosperms: A Lower Cretaceous (Valanginian-Hauterivian) fruit-like reproductive structure. AMERICAN JOURNAL OF BOTANY 2009; 96:323-335. [PMID: 21628191 DOI: 10.3732/ajb.0800295] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
A remarkably diverse Lower Cretaceous (Valanginian-Hauterivian) flora at Apple Bay, Vancouver Island, preserves seed plants at an important time of floristic evolutionary transition, about the same time as the earliest flowering plant megafossils. The fossils are permineralized in carbonate concretions and include tetrahedral seeds within cupule- or carpel-like structures. These enclosing structures, composed of elongate sclerenchyma cells with spiral thickenings that grade externally to a few layers of parenchyma, are vascularized by one collateral vascular bundle and lack trichomes. They apparently broke open to release the tightly enclosed seeds by valves. Seeds are similar to those of the Triassic seed fern Petriellaea, but are about 100 million years younger and differ in size, vascularization, integumentary anatomy, seed attachment, and number of seeds/cupule. These new seeds are described as Doylea tetrahedrasperma gen. et sp. nov., tentatively assigned to Corystospermales. Inverted cupules are reminiscent of an outer angiosperm integument rather than a carpel. Like fruits, cupules opened to release seeds at maturity, thereby foretelling several aspects of angiospermy. They show that nearly total ovule enclosure, a level of organization approaching angiospermy, was achieved by advanced seed ferns during the Mesozoic.
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Affiliation(s)
- Ruth A Stockey
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9
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12
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Rothwell GW, Crepet WL, Stockey RA. Is the anthophyte hypothesis alive and well? New evidence from the reproductive structures of Bennettitales. AMERICAN JOURNAL OF BOTANY 2009; 96:296-322. [PMID: 21628190 DOI: 10.3732/ajb.0800209] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Bennettitales is an extinct group of seed plants with reproductive structures that are similar in some respects to both Gnetales and angiosperms, but systematic relationships among the three clades remain controversial. This study summarizes characters of bennettitalean plants and presents new evidence for the structure of cones and seeds that help clarify relationships of Bennettitales to flowering plants, Gnetales, and other potential angiosperm sister groups. Bennettitales have simple mono- or bisporangiate cones. Seeds are borne terminally on sporophylls. They have a unique structure that includes a nucellus with a solid apex, no pollen chamber, and a single integument, and they are clearly not enclosed by a cupule or other specialized structures. Such features differ substantially from Gnetales, flowering plants, and the seed fern Caytonia, providing no compelling evidence for the origin of the angiospermous carpel. Cladistic tests were performed to assess the strength of the "anthophyte hypothesis" and possible relationships of Bennettitales, Gnetales, and Caytonia to flowering plants. Our results do not support the anthophyte hypothesis for the origin of angiosperms by a transformation of fertile organs that were already aggregated into a cone or flower-like structure. However, the anthophyte topology of the seed plant tree continues to be supported by morphological analyses of living and extinct taxa.
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Affiliation(s)
- Gar W Rothwell
- Department of Environmental and Plant Biology, Ohio University, Athens, Ohio 45701 USA
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13
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Taylor EL, Taylor TN. Seed ferns from the late Paleozoic and Mesozoic: Any angiosperm ancestors lurking there? AMERICAN JOURNAL OF BOTANY 2009; 96:237-251. [PMID: 21628187 DOI: 10.3732/ajb.0800202] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Five orders of late Paleozoic-Mesozoic seed ferns have, at one time or another, figured in discussions on the origin of angiosperms, even before the application of phylogenetic systematics. These are the Glossopteridales, Peltaspermales, Corystospermales, Caytoniales, and Petriellales. Although vegetative features have been used to suggest homologies, most discussion has focused on ovulate structures, which are generally interpreted as megasporophylls bearing seeds, with the seeds partially to almost completely enclosed by the megasporophyll (or cupule). Here we discuss current information about the reproductive parts of these plants. Since most specimens are impression-compression remains, homologizing the ovulate organs, deriving angiospermous homologues, and defining synapomorphies remain somewhat speculative. Although new specimens have increased the known diversity in these groups, a reconstruction of an entire plant is available only for the corystosperms, and thus hypotheses about phylogenetic position are of limited value. We conclude that, in the case of these seed plants, phylogenetic analysis techniques have surpassed the hard data needed to formulate meaningful phylogenetic hypotheses. Speculation on angiosperm origins and transitional stages in these fossils provides for interesting discussion, but currently it is still speculation, as the role of these groups in the origin of angiospermy continues to be cloaked in Darwin's mystery.
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Affiliation(s)
- Edith L Taylor
- Department of Ecology and Evolutionary Biology, and Natural History Museum and Biodiversity Research Center, University of Kansas, Lawrence, Kansas 66045-7534 USA
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Frohlich MW, Chase MW. After a dozen years of progress the origin of angiosperms is still a great mystery. Nature 2008; 450:1184-9. [PMID: 18097399 DOI: 10.1038/nature06393] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2007] [Accepted: 10/18/2007] [Indexed: 11/09/2022]
Abstract
Here we discuss recent advances surrounding the origin of angiosperms. Putatively primitive characters are now much better understood because of a vastly improved understanding of angiosperm phylogenetics, and recent discoveries of fossil flowers have provided an increasingly detailed picture of early diversity in the angiosperms. The 'anthophyte theory', the dominant concept of the 1980s and 1990s, has been eclipsed; Gnetales, previously thought to be closest to the angiosperms, are related instead to other extant gymnosperms, probably most closely to conifers. Finally, new theories of flower origins have been proposed based on gene function, duplication and loss, as well as on morphology. Further studies of genetic mechanisms that control reproductive development in seed plants provide a most promising avenue for further research, including tests of these recent theories. Identification of fossils with morphologies that convincingly place them close to angiosperms could still revolutionize understanding of angiosperm origins.
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Crane PR, Herendeen P, Friis EM. Fossils and plant phylogeny. AMERICAN JOURNAL OF BOTANY 2004; 91:1683-99. [PMID: 21652317 DOI: 10.3732/ajb.91.10.1683] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Developing a detailed estimate of plant phylogeny is the key first step toward a more sophisticated and particularized understanding of plant evolution. At many levels in the hierarchy of plant life, it will be impossible to develop an adequate understanding of plant phylogeny without taking into account the additional diversity provided by fossil plants. This is especially the case for relatively deep divergences among extant lineages that have a long evolutionary history and in which much of the relevant diversity has been lost by extinction. In such circumstances, attempts to integrate data and interpretations from extant and fossil plants stand the best chance of success. For this to be possible, what will be required is meticulous and thorough descriptions of fossil material, thoughtful and rigorous analysis of characters, and careful comparison of extant and fossil taxa, as a basis for determining their systematic relationships.
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Affiliation(s)
- Peter R Crane
- Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AB, UK
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Abstract
The Mostly Male theory is the first to use evidence from gene phylogenies, genetics, modern plant morphology and fossils to explain the evolutionary origin of flowers. It proposes that flower organization derives more from the male structures of ancestral gymnosperms than from female structures. The theory arose from a hypothesis-based study. Such studies are the most likely to generate testable evolutionary scenarios, which should be the ultimate goal of evo-devo.
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Affiliation(s)
- Michael W Frohlich
- Department of Botany, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK.
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