Rhabdoxylon taiyuanense n. sp.: A new botryopterid fern from the Lower Permian of Shanxi Province, North China

This paper described a new early leptosporangiate fern occurring in the Lower Permian coal balls from Shanxi Province, North China. The fossil materials include stems, attached and detached petioles and roots, belonging to a same kind of plant. Stems are relatively small in diameter and branch dichotomously. They possess a haplostele with metaxylem tracheids decreasing outward in diameter and showing uniseriate scalariform thickenings. There are no distinguished protoxylem groups in the xylem cylinder. Cortex is parenchymatous and can be divided into three zones according to cell size. Petiolar traces bear different shapes in cross section and show a spiral diverging sequence. Petioles are circular in cross section and cortical cells are much smaller than those of stems. Petiolar traces and petioles possess a single protoxylem group at the adaxial side of the xylem strand. Root traces originate from the cauline stele and go through the cortex in a way perpendicular or oblique to the cauline stele. These characters show great similarities to the genus Rhabdoxylon but are not consistent with its any known species, so it is necessary to create a new species Rhabdoxylon taiyuanense n. sp. for the present plant. The new species probably possesses an upright habit. This is the first report of the existence of the genus Rhabdoxylon in the Cathaysian Flora. The discovery of a new type of the Palaeozoic leptosporangiate fern in China has led to reevaluation of the systematic relationships among species of the Botryopteridaceae.