中国科学院南京地质古生物研究所机构知识库

A unique coniferous woody stem Shenoxylon mirabile gen. nov. et sp. nov. is described from the very late late Permian Changhsingian (Lopingian) Sunjiagou Formation of the Shitanjing coalfield, northern China. The silicified decorticated stem is characterized by a complex pith in the broad (7 mm) eustelic vascular system, thick secondary xylem cylinder and helically arranged leaf traces. The heterogeneous pith consists of a densely arranged sclerified intramedullary sheath that separates the loosely arranged central parenchyma and peripheral sclerified cells into three prominent zones. The primary xylem strands show endarch maturation, the tracheids from the protoxylem to metaxylem showing annular to scalariform/reticulate thickenings. The secondary xylem is pycnoxylic; uniseriate bordered pits are continuous or individually spaced on the radial walls of tracheids, with partially biseriate, alternate or occasionally opposite; the cross-fields show one or two cupressoid pits; ray cells are parenchymatous with smooth walls; axial parenchyma is developed. Growth-rings are present and false rings are frequently developed throughout the secondary xylem; resin canals are absent. The leaf traces are composed of monarch vascular bundles and of circular to longitudinally elongate shape in cross section; they originate from the periphery of the pith and pass through the whole xylem cylinder nearly horizontally. The frequent occurrences of false rings are interpreted as ecophysiological responses of the plant to the environmental turbulences during the latest Permian terrestrial ecosystem. (C) 2011 Elsevier B.V. All rights reserved.