Polythecophyton demissum, gen. et sp. nov., a new plant from the Lower Devonian (Pragian) of Yunnan, China and its phytogeographic significance
详细信息 查看全文
- 作者：Shou-gang ; Hao ; Gensel ; Patricia G. ; De-ming ; Wang
- 关键词：Polythecophyton ; new genus ; Posongchong flora ; Lower Devonian ; Yunnan of China
- 刊名：Review of Palaeobotany and Palynology
- 出版年：2001
- 出版时间：August, 2001
- 年：2001
- 卷：116
- 期：1-2
- 页码：55-71
- 全文大小：928 K
文摘
A new genus and species, Polythecophyton demissum Hao, Gensel and Wang, is described from the Posongchong Formation of Pragian age in the Wenshan district of southeastern Yunnan. This plant consists of major axes, which divide anisotomously to produce irregularly to helically arranged lateral branches. Lateral branches dichotomize once, producing a pair of curved axes; each may dichotomize again, and then produce a series of short, pendulous, lateral fertile systems via unequal bifurcations. Each fertile system may initially bifurcate, and then each component bears 3–4 alternately arranged, short axes terminated by numerous slender fusiform sporangia borne in pairs or in groups of three or four. Collectively, the fertile system is umbrella-like in outline and sometimes bilaterally symmetrical, with a convex upper contour and nearly even lower margin because all sporangia terminate at almost the same level. In some characteristics i.e. shape of the fertile system, type and attachment of sporangia, Polythecophyton shows similarities with Hedeia Cookson, but it differs in its more complex, mostly pinnate distal branching pattern and its pendulous form. Polythecophyton also is similar in some aspects of branching, sporangial morphology, and sporangial attachment to aneurophytalean progymnosperms; in the absence of anatomy and vegetative regions, we currently regard it as Euphyllophytina incertae sedis sensu . Given its early age, it is of interest in considering evolution of progymnospermous branching patterns, especially in fertile regions. The discovery of this new plant in China demonstrates further variation of plant traits in the northeastern Gondwana phytogeographic region. The architecture of the new plant is of interest because of the sparsity of plants allied to euphyllophytes in this region and its resemblance to aneurophytaleans.