AOBPreview originally published online on June 30, 2004
Annals of Botany 2004 94(2):281-288; doi:10.1093/aob/mch138
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Annals of Botany 94/2, © Annals of Botany Company 2004; all rights reserved
A New Permian Gnetalean Cone as Fossil Evidence for Supporting Current Molecular Phylogeny
Tianjin Institute of Geology and Mineral Resources, Chinese Academy of Geological Sciences No. 4, 8th Road, Dazhigu, 300170 Tianjin, China
* For correspondence. E-mail zwq{at}mail.zlnet.com.cn
Received: 17 October 2003 Returned for revision: 16 January 2004 Accepted: 6 April 2004 Published electronically: 30 June 2004
• Background and aims The order Gnetales has been the central focus of controversy in seed plant phylogeny. Traditional treatment of morphology supports the anthophyte hypothesis with Gnetales sister to angiosperms but current molecular data reject this hypothesis. A new fossil gnetalean cone, Palaeognetaleana auspicia gen. et sp. nov., is reported from the Upper Permian in North China, and its phylogenic implications are considered.
• Methods Samples of cones from the upper part of the Upper Permian redbeds of Baode section, northwestern Shanxi Province, China, were examined.
• Key results The cone is characterized by its unusual nature of reproduction that combines features of post-Triassic gnetaleans and some of the Palaeozoic conifers. It is made up of a number of imbricate axillary units, each simply formed by an ovule and a subtending bract, which may be comparable with the axillary seed-scale complex of some of the Palaeozoic conifer cones. The cone exhibits at least a partially bisexual character that appears to have pollen sacs with monosulcate ribbed pollen grains and sessile, asymmetric, and radiospermic ovules. The ovule has an integument of three envelopes: an outer one of pointed scales; a middle sclerified one; and an inner cuticle that extends upward into a micropyle with an oblique tip.
• Conclusions The new Permian cone has unequivocal affinity with the Gnetales. The fossil has considerably extended the divergence time of the Gnetales from 140 (210?) back to 270 myr ago and, therefore, provides the first significant fossil evidence to support the current conclusion based on molecular data of seed plants, i.e. monophyletic gymnosperms, comprising the Gnetales are closely related to conifers.
Key words: Palaeognetaleana auspicia (gen. et sp. nov.), Gnetales, bisexual fossil cone, phylogeny of seed plants, radiation of gymnosperms, molecular data, Late Permian, North China
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