Sclerospiroxylon xinjiangensis nov. sp., a gymnospermous wood from the Kungurian (lower Permian) southern Bogda Mountains, northwestern China: Systematics and palaeoecology

Abstract

A new silicified wood, Sclerospiroxylon xinjiangensis Wan, Yang et Wang nov. sp., is described from the Cisuralian (lower Permian) Hongyanchi Formation in southeast Tarlong section, Turpan City, Xinjiang Uygur Autonomous Region, northwestern China. The fossil wood is composed of pith, primary xylem and Prototaxoxylon-type secondary xylem. The pith is solid, circular, heterocellular, with sclerenchyma and parenchyma. The primary xylem is endarch to mesarch, with scalariform thickenings on tracheid walls. The secondary xylem is pycnoxylic, composed of tracheids and parenchymatous rays. Growth rings are distinct. Tracheids have mostly uniseriate, partially biseriate araucarian pitting on their radial walls. Helical thickenings are always present on both the radial and the tangential walls. Rays are 2–14 cells high, with smooth walls. There are 2 to 7, commonly 2 to 4 cupressoid pits in each cross-field. Leaf traces suggest that S. xinjiangensis nov. sp. was evergreen with a leaf retention time of at least 15years. Based on the sedimentological evidence, growth rings within the S. xinjiangensis nov. sp. could have been caused by seasonal climatic variations, with unfavorable seasons of drought or low temperature. Low percentage of latewood in each growth ring is probably due to the intensity of climatic seasonality and/or long leaf longevity.