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J Integr Plant Biol, 1990, 32 (12): -, Research Article
New Observations on Leptophloeum rhombicum from the upper Devonian of Hubei, China
Geng Bao-yin
A petrified stem of Leptophloeum rhombicum is described from the Huangjiadeng Formation of the Upper Devonian in Changyang, Hubei. In the xylem of the axis, the secondary xylem is not preserved, the greatest part of the primary xylem is composed of metaxylem tracheids that are scalariform and have Williamson's striations. Based on their connections between adjacent transverse bars Witliamson's striations would be considered as a part of the secondary wall material. The small protoxylem tracheids form vertical ridges at the periphery of primary xylem cylinder. In cross section, the ridges appear as small radiating teeth of protoxylem. It provides further evidence that primary xylem in Leptophloeum rhombicum is similar to that in Carboniferous lepidodendrid lycopods. The opinion that the systematic position of Leptophloeum should be transferred from the Protolepidodendrales to the Lepidodendrales could be accepted and reaffirmed.
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