CORDAITALEAN SEED PLANTS FROM THE EARLY PERMIAN OF NORTH CHINA. III. RECONSTRUCTION OF THE SHANXIOXYLON TAIYUANENSE PLANT

The third of three whole-plant cordaitaleans we reconstructed from a single Early Permian locality in northern China is Shanxioxylon taiyuanense. The name is based on the stem S. taiyuanense B. Tian & S.-J. Wang emend. S.-J. Wang & J. Hilton, which has a large septate pith and endarch cauline bundles that generate mesarch leaf traces that dichotomize at the pith margin. The comparatively small, elongate leaves with few veins and thickened margins are assigned to Cordaites taiyuanensis S.-J. Wang & B. Tian emend. S.-J. Wang and J. Hilton, which is here nomenclaturally typified after a previous invalid publication. Fertile axes are diamond shaped in transverse section, bearing in a tetrastichous arrangement numerous bracts and secondary shoots that consist of basal leaflike sterile scales and apically concentrated fertile scales. Male cones of Cordaitanthus ximinensis S.-J. Wang & B. Tian consist of 20-30 sterile scales and an unknown number of fertile scales that produce pollen assignable to Florinites. Female cones of Cordaitanthus xishanensis S.-J. Wang & B. Tian consist of 30-35 sterile scales and 5-10 fertile scales that bear ovules of Cardiocarpus taiyuanensis J. Hilton, S.-J. Wang,& B. Tian, the smallest species described in this ovule genus. The correlation of these constituent organ species into a whole-plant species received little assistance from organic connection, which was confined to only one equivocal physical attachment between the pollen cone C. xishanensis and the ovule Cardiocarpus taiyuanensis. The presence of sclerenchyma strands allows histological correlation between the leaf species Cordaites taiyuanensis and the sterile scales of both the pollen cone and the ovulate cone. Positive association among the constituent organ species within the deposits also offers limited support for this reconstruction, as the individual organ species, other than leaves, are insufficiently frequent to allow statistical analysis. Thus, the reconstruction of S. taiyuanense relies partly on previous successes-specifically, better-supported reconstructions of two conceptual whole-plant cordaitaleans co-occurring at the locality, Shanxioxylon sinense and Cordaixylon tianii-and partly on the characteristically poor preservation of the components of S. taiyuanense, which are assumed to have been transported into the depositional environment from a drier environment of growth. The three whole-plant cordaitaleans are compared for the rigor of their respective reconstructions, and nomenclatural consistency is achieved by describing the leaves of S. sinense as a new organ species, Cordaites sinensis R. M. Bateman & S.- J. Wang.