维管植物叶子的起源

陆生维管植物中叶子的出现和早期演化是影响到整个地球生命的重要事件。许多植物化石被做了研究，但对叶子究竟什么时候、以什么样的形态是早出现在陆地上，人们仍有不同的看法。早在本世纪初Ｊｅｆｆｅｒｅｙ把叶子分为小型叶和大型叶，Ｂｏｗｅｒ进一步赋予它们系统发育上的含义。依据在劳伦大陆泥盆系地层中发现的化石，人们对小型叶起源的“突起学说“和大型叶起源的“顶枝学说“做出了相应的解释。特别是在大型叶演化系列中建立

Origin of Leaves in Vascular Plants

The origin and evolution of leaves was an important event in plant evolution andhaS affected all other land lives on the earth. Much remains to be learnt.however,ashow they first appeared and how they evolved are still unclear, Traditionally leaveshave been divided into two groups: microphyll and megaphyll. The forlner was evolvedfrom appendages suggested by enation theory and the latter arised from as Zimmermannsuggests in his telome theory. And Sawdonia-Asteroxylon-Drepanophycus line of micro- phyll as well trimerophyte-aneurophyte-seed line of megaphyll have been established onLaurussia(that today includes central and northern Europe, Greenland and North Ame- rica). Do these lines conform to condition of south-eastern Yunnan, a part of SouthChina Block?The answer is both yes and no. Discalis longistipa reported from theYunnan is considered as a member of evolution series of microphyll, and characterizedby radiated arrangement of sporangia may replaced Sawdonia of the series. And studiesof Eophyllophyton bellum of the area cast a new light on origin and evolution ofmegaphyll. It shows that much divided,laminate leaves had happened by the middleLower Devonian(Siegenian) and megaphyll evolved no later than the microphyll. Obvio-usly, it is prior to the known appearence of the more primitive members of the trime-rophyte-aneurophyte plant line, on the other hand, the fertile characters of E. bellumdiffer from that of trimerophyte plant on Laurussia. Thus E. bellum may represent another line of evolution parallel to and distinct from the trimerophyte line, and landvascular plants may be separately occured on the separate blocks and evolved intiallyalong the own line during Silurian-Early Devonian in age.