Abstract

Phylogenetic relationship among seed plants recently obtained with molecular genetics fails to reveal the evolutionary steps of the formation of the basic morphotype of flowering plants. This task can be solved via morphological functional modeling of the first steps of the formation of flowering plants based on appropriate morphotypes in extant flora, irrespective of their genetic kinship. For instance, Gnetales adhere phylogenetically to conifers, but the genus Gnetum is appreciated for its numerous features convergent with angiosperms and can be used as a model of the morphological state of the angiosperm ancestor. A morphological analysis of the available data shows that the true angiosperm ancestor must have differed from Gnetum in some important respects, e.g., it must have had a more primitive xylem and bisexual fructifications. Aquatic intermediate stage modeled by water lilies is needed as a “bridge” that connects this ancestral condition with a full-fledged flowering plant. This intermediate stage differed from the extant water lilies in some crucial respects, e.g., it retained a cambium and possessed small flowers. The appearance of perianth with corolla is supposed to be possible at this aquatic stage only because it is water-wasteful. The scenario employs the concept of a megasporangia-bearing shoot, which is an alternative to the more common concept of a megasporangia-bearing leaf.

中文翻译：

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Gnetum 和睡莲类作为开花植物形态起源情景的模型

摘要

最近用分子遗传学获得的种子植物之间的系统发育关系未能揭示开花植物基本形态形成的进化步骤。这项任务可以通过基于现有植物群中适当形态型的开花植物形成的第一步的形态学功能建模来解决，而不管它们的遗传亲缘关系如何。例如，Gnetales 在系统发育上依附于针叶树，但Gnetum属因其与被子植物收敛的众多特征而受到赞赏，并可用作被子植物祖先形态状态的模型。对现有数据的形态分析表明，真正的被子植物祖先一定与Gnetum不同在一些重要的方面，例如，它一定有更原始的木质部和双性果实。需要以睡莲为模型的水生中间阶段作为连接这种祖先条件与成熟开花植物的“桥梁”。这个中间阶段在一些关键方面与现存的睡莲不同，例如，它保留了形成层并拥有小花。在这个水生阶段，花被和花冠的出现应该是可能的，只是因为它浪费水。该场景采用了带大孢子囊的枝条的概念，这是对更常见的带大孢子囊的叶子概念的替代。