Hao, Shougang , Xue, Jinzhuang .
Roots and leaves in the Early Devonian vascular plants.
In the early years, it was generally suggested that early vascular plants lack any kind of true rooting structures and leaves (particularly megaphyll). It was suggested that they had only rhizome bearing rhizoids, for which the rhyniophytes of the Rhynie Chert seem to offer some evidence. However, current data indicate that at least some of the early vascular plants bear rooting systems. The zosterophytes have downwardly directed rooting system. The fibrous-like rooting system of Zosterophyllum shengfengense (Lochkovian age) is about 2 cm in length. The basal lycopsids Asteroxylon and Drepanophycus have branched adventitious roots. It is also reasonable to suggest that euphyllophytes bear root or rooting systems. By the Early Devonian, true leaves (microphyll and megaphyll) have evolved, except for the leafless zosterophytes and rhyniophytes. In Australia, microphylls are represented on remains of Baragwanathia of Late Silurian age, and a questionable microphyll plant has been reported from Pridoli deposits of North Xinjiang, China. Leaves are represented by Drepanophycus from the Upper Lochokovian of Germany and Asteroxylon from the Pragian Rhynie Chert. Typical sporophyll has occurred in the Posongchong flora (e.g. in Zhenglia). Psilophyton and the early ferns or fernlike plants are alike in having three-dimensional dichotomous telome trusses, corresponding or foreshadowing the later appearance of planated and webbed megaphylls. Then true megaphylls characterized by reduced branching trusses (i.e., Estinnophyton) and laminate structures with a complex venation (i.e., Eophyllophyton) have evolved in the northeastern Gondwana phytogeographic unit. It is noteworthy that some Early Devonian plants bear leaf-like appendages or leaves covering sporangia, but their axes are naked without any leaves (e.g., Adoketophyton). This implies that these leaf-like structures might have performed a protective and nutritious function for their sporangia.
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1 - School of Earth and Space Sciences, Peking University, Beijing 100871, P.R. China
Presentation Type: Poster:Posters for Sections
Location: Hall A/Convention Center
Date: Monday, August 2nd, 2010
Time: 5:30 PM