志留纪—早泥盆世维管植物的系统发育、幕式演化和地理分布:植物大化石证据

尽管近年来对志留纪—早泥盆世陆生维管植物系统发育的认识取得了很大进展,但是目前对多囊蕨类、莱尼蕨类、工蕨类的界定和类群划分尚有分歧,工蕨类和石松类的姐妹群关系仍有疑问,真叶植物基部类群有待深入研究。志留纪至早泥盆世的维管植物演化可划分为2幕,即前布拉格期序幕阶段和布拉格期爆发阶段。维管植物主要分支在第1幕均处于萌芽状态,仅出现个别先驱型分子;第2幕为维管植物分支爆发式演化的主幕。在布拉格期,规则叶序、孢子叶、似叶球状结构等石松类的典型性状最早显现,真叶植物发生明显的分支分化,大型叶及其同源器官(枝叶复合体)多次独立起源,孢子囊和叶性结构的发育相关性在多个支系中趋同演化出现。古植物地理方面,在东北冈瓦纳区的华南地区,工蕨类以孢子囊螺旋排列的类型为主,真叶植物在布拉格期显示出高度的多样性和分异度;在劳俄区,工蕨类中孢子囊成列排列的类型较为丰富,真叶植物的大量出现要晚于华南地区。羊角蕨纲、拟库克逊蕨类、莱尼蕨目的分支演化可能主要发生在南劳俄和西北冈瓦纳等中、高纬度地区。工蕨类、石松类和真叶植物的分支演化和地理辐射可能遵循“走出热带”模式,它们在低纬度地区最早发生分化并快速辐射;维管植物主要分支在布拉格期的爆发式演化,主要是热带植物群革新演化的贡献。

Phylogeny,episodic evolution and geographic distribution of the Silurian-Early Devonian vascular plants:Evidences from plant megafossils

Much progress has been made in the understanding of the phylogeny of Silurian-Early Devonian vascular land plants during the past years. However,no consensus has been reached considering the delimitation and subdivision of polysporangiophytes,rhyniopsids,and zosterophyllopsids;the sister-group relationship between zosterophyllopsids and lycopsids is questioned;detailed studies of basal euphyllophytes are needed. The evolutionary history of the Silurian-Early Devonian vascular plants can be divided into two phases:The pre-Pragian prelude phase and the Early Devonian Pragian explosion(burst)phase. The first phase is characterized by initial emergences of representatives of vascular plant major clades. The second is the main phase which witnessed explosive radiation of vascular plant clades. During the Pragian,typical features of lycopsids such as regular phyllotaxy,sporophylls,and strobilus-like structures appeared;the diversification of euphyllophyte lineages occurred;megaphylls and their homologous structures(branch-leaf complexes)evolved multiple times independently;and developmental interrelationship between sporangia and leafy structures convergently established in different lineages. In South China of the northeastern Gondwanan phytogeographic unit,zosterophyllopsids were dominated by those with spirally arranged sporangia and euphyllophytes showed high diversity and disparity during the Pragian,while in the Laurussian phytogeographic unit,zosterophyllopsids with rowed sporangia were abundant and the appearance of comparable euphyllophytes occurred later than in South China. The cladogenesis of horneophytopsids,cooksonioids,and rhynialeans might have mainly occurred at middle and high paleolatitudes such as southern Laurussia and northwestern Gondwana. The cladogenesis and biogeographic radiation of zosterophyllopsids,lycopsids,and euphyllophytes may accord with the “out of the tropics”model,that is,these groups diversified and rapidly radiated earlier at low paleolatitudes;the explosion of vascular plant clades in Pragian was mainly contributed by the evolutionary novelty of tropical floras.