Comparative Anatomy of the Seed Coats of Gnetum and Their Probable Evolution

Rodin, Robert J.; Kapil, R. N.

doi:10.2307/2440819

Cited by 17 publications

(22 citation statements)

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“…Further, the numerous supportive strands in the sclerenchymatous zone form a pattern with dichotomies and anastomoses, which is very similar to that formed by vascular bundles in the "endotesta" of Gnetum [44]. In the Gnetales, vascular bundles are absent in the integument but present in the seed envelopes [24], which supports our interpretation that the supportive strands of Siphonospermum are originally derived from the seed envelope.…”

Section: Discussionsupporting

confidence: 77%

A new Early Cretaceous relative of Gnetales: Siphonospermum simplex gen. et sp. nov. from the Yixian Formation of Northeast China

Rydin

Friis

2010

BMC Evol Biol

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BackgroundKnowledge on fossil and evolutionary history of the Gnetales has expanded rapidly; Ephedra and ephedroids as well as the Gnetum-Welwitschia clade are now well documented in the Early Cretaceous. However, hypotheses on evolutionary relationships among living and fossil species are hampered by restricted knowledge of morphological variation in living groups and recent studies indicate that gnetalean diversity and character evolution may be more complex than previously assumed and involve additional extinct groups (Bennettitales, Erdtmanithecales and unassigned fossil taxa).ResultsHere we describe a new fossil related to Gnetales, Siphonospermum simplex from the Early Cretaceous Yixian Formation, an impression/compression of a reproductive shoot. The slender main axis bears one pair of opposite and linear leaves with primary parallel venation. The reproductive units are ovoid, without supporting bracts and borne on one median and two lateral branches. The most conspicuous feature of the fossil is the long, thread-like micropylar tube formed by the integument. Each ovule is surrounded by two different layers representing one or two seed envelopes; an inner sclerenchymatous layer and an outer probably parenchymatous layer.ConclusionsThe vegetative and reproductive features of Siphonospermum simplex exclude a relationship to any other group than the Gnetales. A combination of opposite phyllotaxis, linear leaves and ovules surrounded by seed envelope(s) and with a long exposed micropylar tube are known only for extant and extinct Gnetales. Siphonospermum simplex constitutes a new lineage within the Gnetales. Its morphology cannot be directly linked to any previously known plant, but the organization of the reproductive units indicates that it belongs to the Gnetum-Welwitschia clade. Based on the absence of cone bracts and the inferred histology of the seed envelope(s) it could be related to Gnetum, however, there are also affinities with the ephedran lineage, some of which are likely plesiomorphic features, others perhaps not. Phylogeny and character evolution in the Bennettitales, Erdtmanithecales and Gnetales are currently only partly understood and under debate; the exact systematic position of Siphonospermum simplex, i.e., its position within the Gnetales, cannot be resolved with certainty.

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Section: Discussionsupporting

confidence: 77%

A new Early Cretaceous relative of Gnetales: Siphonospermum simplex gen. et sp. nov. from the Yixian Formation of Northeast China

Rydin

Friis

2010

BMC Evol Biol

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“…This double vascular supply to the ovules is not known to occur in any of the other taxa considered in this study. Rodin and Kapil (1969) have compared the ovule vasculature of Gnetum with that of Pachytesta, but under the interpretation given here (character 9.33) only the inner envelope of a Gneturm ovule is a true integument, and therefore the two outer layers do not have homologues in cycads or medullosans. In Lagenostoma (Lyginopteris) there is a unitegmic ovule with a radial vascular supply inside a vascularized cupule.…”

Section: Phylogenetic Relationships Of Extantmentioning

confidence: 91%

“…More detailed examinations of the ovules in primitive Bennettitales are required, but here I interpret this platyspermy as primitive for the Bennettitales on the basis that the ovules resemble those of Mesozoic seed ferns, Callistophyton, cordaites, and other groups mentioned above. The integument of Gnetum ("endotesta" of Rodin & Kapil, 1969) has a well-developed radial vascular system; and Welwitschia ovules are unvascularized and radiospermic.…”

Section: Phylogenetic Relationships Of Extantmentioning

confidence: 99%

Phylogenetic Analysis of Seed Plants and the Origin of Angiosperms

Crane¹

1985

Annals of the Missouri Botanical Garden

548

389

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Missouri Botanical Garden Press is collaborating with JSTOR to digitize, preserve and extend access to Annals of the Missouri Botanical Garden. ABSTRACT Principles of phylogenetic analysis (cladistics) are introduced with an examination of relationships among extant genera of Gnetales. The Gnetales can be supported as a monophyletic group, with Gnetum and Welwitschia more closely related to each other than either is to Ephedra. Characters of the progymnosperm Archaeopteris and 19 extinct and extant seed plant taxa are then reviewed as a basis for a cladistic analysis of their interrelationships. The seed plant taxa included are: Bennettitales are also presented. Results suggest that seed plants are a monophyletic group, and Lyginopteris is resolved as the sister taxon to all other seed plants considered. The cordaites, Cordaixylon and Mesoxylon, along with Lebachia, extant conifers, and Ginkgo constitute a monophyletic group. Pentoxylon is the sister taxon to Bennettitales, and the Gnetales are the sister group to angiosperms. Together the Gnetales plus the angiosperms form the sister group to the Bennettitales plus Pentoxylon. If the outer integument of bennettitalean and angiosperm ovules is interpreted as homologous with the "cupule" of Caytonia and corystosperms, then the corystosperms are resolved as the sister group to the Bennettitales plus Pentoxylon plus Gnetales plus angiosperm clade. Under this interpretation all the seed plant taxa considered except Lyginopteris, cycads, and medullosans are part of a single clade in which flattened seeds and saccate pollen are primitive. The principal difficulties with the cladistic analysis concern necessary inferences on unknown characters in certain plants, and the current absence of a large base of comparative data. Results of the analysis suggest that the seed ferns as currently circumscribed are not a meaningful group for phylogenetic purposes and permit an evaluation of the possible phylogenetic position of Eremopteris, Nystroemia, Spermopteris, Phasmatocycas, Vojnovskiales, Leptostrobus, and several other enigmatic groups of plant fossils. Comparison of the phylogenetic analysis with previous theories of angiosperm origin shows that it reconciles the ideas of Arber and Parkin, that Bennettitales and Gnetales are closely related to flowering plants, with more recent hypotheses that invoke Caytonia and corystosperms as highly relevant to the angiosperm problem. The results suggest that increased understanding of Triassic Bennettitales, Gnetales, and corystosperms will be of maximum interest in further elucidating the phylogenetic relationships of flowering plants.' This paper is dedicated to the late Dr. P. D. W. Barnard, who...

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“…However, a mechanism by which long-distance dispersal over oceans might occur has to our knowledge not been clearly demonstrated. Some species of Gnetum have a corky layer in the seed (Maheshwari & Vasil, 1961;Rodin & Kapil, 1969), possibly allowing them to float. Nevertheless, with the potential exception of the origin of the Asian clade, we find no clear indication in our results that dispersal over oceans, such as the contemporary Atlantic, Pacific and Indian Oceans, has ever occurred.…”

Section: Version Of Recordmentioning

confidence: 99%

“…However, some deep nodes are poorly supported and several questions remain, mainly regarding deep divergences, the phylogenetic placement of previously unsampled taxa, and species delimitation. Furthermore, although Gnetum is well studied in several respects, e.g., regarding embryogenesis (Coulter, 1908;Augustine & D'Souza, 1997;Friedman & Carmichael, 1998;Haycraft & Carmichael, 2001), life history (Lotsy, 1899;Pearson, 1912;Pearson & Thomson, 1917;Maheshwari & Vasil, 1961), anatomy and morphology (Berridge, 1911;Thoday, 1911Thoday, , 1921Duthie, 1912;Thompson, 1916;Rodin & Kapil, 1969;Fisher & Ewers, 1995;Endress, 1996) and palynology (Hesse, 1980;Gillespie & Nowicke, 1994;Yao & al., 2004;Tekleva & Krassilov, 2009), the data are often based on only one or a few species. Intraspecific variation and parallel evolution of similar traits (both of which are widespread in Ephedra; Ickert-Bond & Wojciechowski, 2004;Rydin & al., 2004Huang & al., 2005;Rydin & Korall, 2009) have thus not been assessed in a modern phylogenetic framework.…”

Section: Introductionmentioning

confidence: 99%

New insights into the evolutionary history of Gnetum (Gnetales)

Hou

Humphreys

Thureborn

et al. 2015

TAXON

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Gnetum (Gnetales: Gnetaceae) constitutes an evolutionarily isolated gymnosperm clade, comprising about 40 species that inhabit tropical areas of the world. While its closest living relative, the monotypic Welwitschia, has a well-documented fossil record from the Early Cretaceous, Gnetum-like fossils are rare and poorly understood. The phylogeny of Gnetum has been studied previously but the distant relationship to outgroups and the difficulty of obtaining plant material mean it is not yet fully resolved. Most species are tropical lianas with an angiospermous vegetative habit that are difficult to find and identify. Here a new phylogeny is presented based on nuclear and chloroplast data from 58 Gnetum accessions, representing 27 putative species, and outgroup information from other seed plants. The results provide support for South American species being sister to the remaining species. The two African species constitute a monophyletic group, sister to an Asian clade, within which the two arborescent species of the genus are the earliest diverging. Estimated divergence times indicate, in contrast with previous results, that the major lineages of Gnetum diverged in the Late Cretaceous. This result is obtained regardless of tree prior used in the BEAST analyses (Yule or birth-death). Together these findings suggest a correlation between early divergence events in extant Gnetum and the breakup of Gondwana in the Cretaceous. Compared to the old stem ages of major subclades of Gnetum, crown nodes date to the Cenozoic: the Asian crown group dates to the Cretaceous-Paleogene (K-Pg) boundary, the African crown group to the mid-Paleogene, and the South American crown group to the Paleogene-Neogene boundary. Although dispersal must have contributed to the current distribution of Gnetum, e.g., within South America and from Southeast Asian islands to the East Asian mainland, dispersal has apparently not occurred across major oceans, at least not during the Cenozoic.

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Comparative Anatomy of the Seed Coats of Gnetum and Their Probable Evolution

Cited by 17 publications

References 0 publications

A new Early Cretaceous relative of Gnetales: Siphonospermum simplex gen. et sp. nov. from the Yixian Formation of Northeast China

A new Early Cretaceous relative of Gnetales: Siphonospermum simplex gen. et sp. nov. from the Yixian Formation of Northeast China

Phylogenetic Analysis of Seed Plants and the Origin of Angiosperms

New insights into the evolutionary history of Gnetum (Gnetales)

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