A new anatomically preserved osmundalean stem Tiania resinus sp. nov. from the Lopingian (upper Permian) of eastern Yunnan, China

Abstract This paper describes an osmundalean stem from the Lopingian (upper Permian) Xuanwei Formation in eastern Yunnan Province, southwestern China. The stem of T . resinus sp. nov. is very small, only ca. 1 cm in diameter, and is characterised by the bi-zoned pith, pith cells typically vertically elongated, ectophloic siphonostele, primary xylem mesarch and 6–8 tracheid thick, a mass of sclerenchymatous cells in the adaxial concavity of the leaf trace and an arch-shaped secretory cell band surrounding the adaxial side of the leaf trace. The stem is compared with the member of Osmundales and is assigned into the genus Tiania of the extinct family Guaireaceae, where it represents the smallest member of the Guiariaceae. Distinctions from Tiania yunnanense include no sclerenchymatous and secretory cells in the primary xylem and the secretory cells in the cortex distributing around the adaxial side of the leaf trace and lead to the establishment of Tiania resinus sp. nov. T. resinus together with the three other species from three genera osmundalean trunk/stem have now been reported from the Upper Permian of eastern Yunnan and western Guizhou, southwestern China. Discovery of the new species enriches the diversity of osmundalean plants from the Cathaysian Flora and offers evidence that the area of eastern Yunnan and western Guizhou may be an centre for the distribution and the early evolution of extinct osmundalean family Guaireaceae.