泥盆纪枝蕨纲的分支系统学研究

枝蕨纲是中泥盆世至早石炭世的一个重要的植物类群。作者对枝蕨纲代表植物进行了尝试性的分支系统学研究。枝蕨纲中可识别出伊瑞蕨目、瘤指蕨目和其他一些过渡类型。伊瑞蕨目和瘤指蕨目演化关系密切,二者分别以营养性末级附枝的顶端回弯和具瘤指蕨型的植物体组构为近裔共性。中国中上泥盆统的Metacladophyton和Polypetalophyton比伊瑞蕨目和瘤指蕨目进化程度要高,可能代表枝蕨纲内的一个新的高级分类单元,以具片化的末级附枝及次生生长为特征。伊瑞蕨目和瘤指蕨目出现在中泥盆世,而以Metacladophyton和Polypetalophyton为代表的进化类型出现在中泥盆世晚期至晚泥盆世早期。从伊瑞蕨目、瘤指蕨目到Metacladophyton和Polypetalophyton,侧生分枝系统显示了从三维的枝系统向似羽片状系统逐渐演化的趋势。

A Cladistic Study on Devonian Cladoxylopsida

Cladoxylopsida is an important plant group spanning from the Middle Devonian to Early Carboniferous.A tentative cladistic study on representative plants of Cladoxylopsida was carried out.Within the Cladoxylopsida,two orders,Iridopteridales and Pseudosporochnales,and other transitional forms can be recognized.The synapomorphies of Iridopteridales and Pseudosporchnales are recurvation of sterile ultimate appendages and Pseudosporochnus-type architecture,respectively.Metacladophyton and Polypetalophyton,from the Mid-Late Devonian of China,show several derived characteristics compared with Iridopteridales and Pseudosporochnales.These two plants,characterized by planate ultimate appendages and secondary growth,might represent a new higher taxon within the Cladoxylopsida.The Iridopteridales and Pseudosporochnales appeared in the Middle Devonian,while some advanced forms representated by Metacladophyton and Polypetalophyton occurred during the late Middle Devonian to early Late Devonian.From Iridopteridales,Pseudoporochnales,to the latter two plants,the lateral branching systems show an evolutionary trend from a three-dimensional pattern to a frondlike one.