Anatomically Preserved Pteridosperm Stems and Rachises From Permian Floras of China

Pteridosperms are common in the Permian floras of China and are known from both vegetative and fertile organs in adpression assemblages and as dispersed ovules and seeds in permineralized assemblages. In contrast, reports of vegetative organs from permineralized assemblages are limited, and in all cases, accounts have not been verified by detailed descriptions nor illustration. Here we report four taxa of pteridosperm stem or rachis from the Permian permineralized floras of China. Coal balls from the Asselian-Sakmarian (Cisuralian) Taiyuan Formation are shown to contain specimens of a medullosan and a lyginopterid pteridosperm. The medullosan rachis has a distinctive collateral organization of vascular bundles interspersed within a crushed parenchymatous ground tissue that also has scattered resin ducts, and it is identified as Myeloxylon Brongniart. The lyginopterid has a vitalized protostelic stem with manoxylic secondary xylem and mesarch xylem maturation and is confirmed as Heterangium sp. 1. From volcaniclastic tuffs from the Wujiapingian-Changhsingian (Lopingian) Xuanwei Formation, a eustelic stem with a parenchymatous pith surrounded by discrete primary xylem strands with a large amount of secondary xylem and a sparganum-type cortex is attributed to the Callistophytalean Callistophyton Delevoryas and Morgan. Finally, from the Changhsingian (Lopingian) Wangjiazhai Formation, another lyginopterid is documented that comprises a pair of protostelic stems with manoxylic secondary xylem and mesarch xylem maturation and is assigned to Heterangium sp. 2. Although accounts are based on low specimen numbers, they provide unequivocal evidence of vegetative pteridosperm genera in the Permian of China that were previously known only from the Pennsylvanian and earliest Permian of Euramerica. In this context, they underline the floristic continuation of wetland plant communities extending from the Carboniferous of Euramerica into the Cisuralian-aged peat-forming mires in North China and the Lopingian of South China. Extending the geographical and stratigraphical ranges of these pteridosperm taxa means that each should now be considered as potentially important to seed plant evolution and phylogeny during the Permian as well as the Carboniferous.