Xue, Jinzhuang , Hao, Shougang , Wang, Deming .
An anatomically preserved lycopsid from Hubei, China, and consideration on tracheid ultrastructure of the early lycopsids.
AN anatomically preserved lycopsid with Longostachys-like morphology is described from the Huangjiadeng Formation (Frasnian of Late Devonian) of Hubei Province, China. The metaxylem tracheids of our present plant are composed of scalariform elements. Its scalariform thickenings are solid, and lack any connecting material between (neither perforate layers nor fimbrils). The solid nature of the thickenings indicates they are homogenous in chemical component; those of Hubeiia are also the same. Our new observations on the published images of Minarodendron, Leptophloeum, and Longostachys, however, have found that their secondary thickened bars appear to be layered, with an inner hollow cavity. It is unknown whether this difference is a reflection of preservation or a reflection of chemical differentiation. Among the known fossil lycopsids bearing scalariform thickenings, only a few of them lack connecting material, such as Chamaedendron and Atasudendron. Our plant is another Devonian representation lacking this structure. On the contrary, most other early lycopsids have been found to possess this structure, showed a continuum of forms from those with a sheet of material interrupted by a number of apertures to those with distinct longitudinal fibrils. It is claimed that the connecting material with various structures in these plants is homologous with and derived from the thin connecting perforate layers of Early Devonian basal plants. Besides the potential phylogenetic implication, the variation in structure and organization of these connecting materials might provide clues to ecological conditions. The diverse tracheid ultrastructures of Devonian lycopsids might demonstrate an adaptive radiation to different environments and represent different trajectories to maximum water conducting efficiency.
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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: Auditorium/Bell Memorial Union
Date: Tuesday, August 1st, 2006
Time: 12:30 PM