Stigmariopsis, Stigmaria asiatica, and the survival of the Sigillaria brardii-ichthyolepis group in the tropics of the late Pennsylvanian and Early Permian

Stigmaria asiatica Jongmans et Gothan was discovered in situ in a volcanic tuff layer between two coal seams in the lowermost Permian rocks of the Wuda coal district in Inner Mongolia, China. The species is characterized by its consistently small axial width of 20–30 mm and the combination of vertical and horizontal orientation of each axis. It is interpreted as being attached below the stigmarian axes of trees of the Sigillaria brardii-ichthyolepis group forming a deeper reaching “stigmariopsid” system. Such a unique two-tier rooting system gave this group advantages over other arboreous (tree-sized) lycopsids of the late Palaeozoic. Trees of the S. brardii-ichthyolepis group could reach deeper water resources and thus survive in wetlands that experienced dry seasons with a lowered water table. This complex underground rooting system appears to be one factor that enabled this group to survive the regional extirpation of arboreous lycopsids at the Moscovian–Kasimovian boundary in Euramerica and at the same time be a major peat-forming plant in Cathaysia.