Supplemental material from "New Mississippian materials of the lycopsid rootstock Stigmaria Brongniart from South China: Evidence for anatomical conservatism in this genus"

The genus <i>Stigmaria</i> Brongniart represents the underground rooting system of arborescent lycopsids, which were important elements in coal-swamp forests during the Carboniferous to Permian periods. The morphology and anatomy of <i>Stigmaria</i> have been extensively studied, mainly based on well-preserved materials from the Pennsylvanian of Euramerica, but knowledge about its pre-Pennsylvanian evolutionary history remains to be expanded. Here, new materials of <i>Stigmaria</i> are described from the Visean (Mississippian) Xiangbai Formation of Longli, Guizhou, southwestern China and are classified into <i>Stigmaria </i>cf.<i> S</i>. <i>ficoides </i>(Sternberg) Brongniart. Our plant is characterized by navel-shaped rootlet scars which are arranged helically around rhizomorphs. Its anatomy shows a mixed solenostele with endarch primary xylem and radially aligned secondary xylem which is divided into wedge-shaped segments by rootlet traces. The primary cortex is divided into five zones, but there is no secondary cortex. Rootlet vascular bundles are triangular monarch, protruding from the inner primary cortex to the rhizomorph surface. Our plant represents one of the two earliest records of <i>Stigmaria</i> with anatomy preserved, the other from the Visean of Glenarbuck, England. These Visean records demonstrate great similarity in anatomy with the Pennsylvanian and Permian materials of <i>Stigmaria ficoides</i>, indicating anatomical conservatism and long-term evolutionary stasis in the genus.