Xuanweioxylon damogouense sp. nov., a gymnosperm stem from the Lopingian (late Permian) of southwestern China and its systematic and paleoecological implications

A new species of permineralized gymnosperm stem is described from volcaniclastic tuffs in Lopingian (late Permian) Xuanwei Formation from eastern Yunnan province, China. The stem comprises well-preserved tissues of the pith, primary and secondary xylem. Pith is divided into a thick-walled parenchymatous peripheral zone and an inner parenchymatous part. Primary xylem strands are numerous and indistinct with mesarch maturation. Secondary xylem is pycnoxylic with scalariform bordered pits on radial tracheid walls, with rays normally uniseriate or partly biseriate. Cross-field pits are mixed and including circular, elliptical and scalariform pitting. Comparisons indicate a close affinity with the contemporaneous plant Xuanweioxylon scalariforme, but differences with it lead to the erection of Xuanweioxylon damogouense sp. nov. We evaluate the systematic affinity of both species of Xuanweioxylon and conclude they represent conifers based on features of their wood anatomy. We consider the Xuanwei Formation includes at least four species of conifer, and show that X. damogouense possessed weak growth rings and false rings that suggest it grew in a climate with low seasonality and occasional periods of drought.