Panxianopteris taeniopteroides gen. et sp. nov., an anatomically preserved taeniopterid leaf from the upper Permian of Guizhou Province, China

Abstract

Taeniopterid leaves with entire margins, prominent midribs and simple or bifurcate lateral veins are present in many Paleozoic and Mesozoic floras globally and were a typical and diverse element in the late Paleozoic equatorial Cathaysian flora. Most taeniopterid leaves are preserved as impression-compression fossils that reveal only information on their morphology and in some cases cuticle structure. Taeniopterid leaves preserved with anatomy are much rarer and have only previously been identified in the Mesozoic. Here we report a taeniopterid leaf from the upper Permian Xuanwei Formation in southwestern China that preserves morphology and anatomy. The leaf is over 18 cm long and 10 cm wide, with the lamina attached to the lateral sides of the midrib. Parallel lateral veins arise from the midrib which has longitudinal ridges on its adaxial surface and two distinct groups of vascular bundles. One group of bundles is adaxially located and arranged in a rough inverted Ω-shape, while the other is abaxially located and arranged in a ring. Individual bundles have endarch primary xylem and secondary xylem. Comparisons with other anatomically preserved taeniopterid leaves allow us to establish Panxianopteris taeniopteroides gen. et sp. nov. This vascular bundle arrangement is most comparable to the rachis of the Triassic Umkomasiales pteridosperm leaf Dicroidium fremouwensis from the Gondwanan flora. P. taeniopteroides is the first anatomically preserved taeniopterid leaf reported from the Paleozoic and the Cathaysian flora, and although its affinity remains enigmatic because it is only known from its isolated leaf, it is likely to be a pteridosperm allied with the Umkomasiales or their ancestral lineage.