科研之友
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摘要
A previous study of the Late Devonian cladoxylopsid Denglongia hubeiensis Xue et Hao provided a detailed morphological description, while new material from the type locality of the Huangjiadeng Formation, Hubei Province, China, reported here reveals details of anatomy. Main axes are actinostelic in transverse sections, showing a primary xylem column with five or six xylem ribs separated by deep embayments. First-order axes have a deeply ribbed primary xylem column with four xylem ribs. Each stelar rib has two permanent, mesarch protoxylem strands near its periphery. Tracheids interpreted as protoxylem show annular or helical thickenings. Metaxylem tracheids have scalariform and elliptical bordered pits. Anatomically, Denglongia is more similar to the iridopteridaleans than to other plants in the actinostele, the peripheral protoxylem strands, the disintegration of protoxylem tracheids, and the pitting pattern of metaxylem tracheids. The phylogeny of the Cladoxylopsida was evaluated by parsimony and Bayesian cladistic analyses. The results showed that the Pseudosporochnales constitute a very robust monophyletic group supported by a suite of characters: the presence of arborescence; digitate branching; straight tips of sterile ultimate appendages; dissected primary xylem; elliptical to strap-shaped primary xylem strands; and sclereids in the cortex. The monophyly of the Iridopteridales is questioned in that the previously suggested defining characters, whorled branching and peripheral protoxylem strands, are considered more plesiomorphic in the cladistic context. The relationship between the iridopteridaleans and the sphenophyllaleans is weakly supported. The Bayesian analysis recognized a tentative "iridopteridalean-based group," in which the iridopteridaleans, Denglongia, Metacladophyton Wang et Geng, Polypetalophyton Geng, and their probable relatives are nested within an unresolved polytomy.
- 出版日期2010-1
- 单位Saskatoon; 北京大学
