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Paleobotanical Section

Xue, Jinzhuang [1], Hao, Shougang [1], Wang, Deming [1], Liu, Zhengfeng [1].

A new protolepidodendralean from the Upper Devonian of Hubei Province, China.

A new herbaceous lycopsid is described from the Xiejingsi Formation (Late Devonian) of Hubei Province, China. Its stems are isotomously dichotomized. Leaves are persistent, and show a four-forked appearance as a result of two successive dichotomies. Leaf bases are circular or slightly elliptical in shape, and arranged in low helices or alternating pseudowhorls. Anatomically, it has a solid exarch primary xylem strand. Protoxylem tracheids are composed of annular elements. Metaxylem tracheids are scalariformly thickened, and between thickened bars present vertical threads generally termed “Williamson’s striations”. Primary phloem forms a narrow band, 4-8 cells thick, surrounding the stele. The cortex is relatively thick, possibly two-zoned. Mesarch leaf traces originate directly from protoxylem points and pass through the cortex with a stable oblique angle. The present plant shows a unique combination of characters, i.e., concurrence of forked leaves and “Williamson’s striations” on the same species, and therefore it is designated as a new stem form-genus. Forked leaves are common in Protolepidodendraceae (Protolepidodendrales) yet have never been described in Lepidodendrales. If we put emphasis on leaf morphology, this plant is more referable to Protolepidodendrales. Thus the discovery of this new plant adds new information to our knowledge about the character variation within Protolepidodendrales, indicating that “Williamson’s striations” occur in Protolepidodendrales as well. Except for the comparable structure in Minarodendron, “Williamson’s striations” have never been reported in Protolepidodendrales before. Additionally, the present plant provides positive evidence from anatomy for the hypothesis proposed by many researchers that the protolepidodendrids and those younger advanced forms are closely related.


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1 - Peking University, Department of Geology, Beijing, 100871, China

Keywords:
Forked leaves
Williamson’s striations
Protolepidodendrales
Late Devonian.

Presentation Type: Poster
Session: 33-61
Location: Salon C, D & E - Gov Ballroom/Hilton
Date: Tuesday, August 16th, 2005
Time: 12:30 PM
Abstract ID:32


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