Phylogeny, morphology, and ecology resurrect previously synonymized species of North American Stereum
AbstractStereum is a globally widespread genus of basidiomycete fungi with conspicuous shelf-like fruiting bodies. Several species have been extensively studied due to their economic importance, but broader Stereum taxonomy has been stymied by pervasive morphological crypsis in the genus. Here, we provide a preliminary investigation into species boundaries among some North American Stereum. The nominal species Stereum ostrea has been referenced in field guides, textbooks, and scientific papers as a common fungus with a wide geographic range and even wider morphological variability. We use ITS sequence data of specimens from midwestern and eastern North America, alongside morphological and ecological characters, to show that Stereum ostrea is a complex of at least three reproductively isolated species. Preliminary morphological analyses show that these three species correspond to three historical taxa that were previously synonymized with S. ostrea: Stereum fasciatum, Stereum lobatum, and Stereum subtomentosum. Stereum hirsutum ITS sequences taken from GenBank suggest that other Stereum species may actually be species complexes. Future work should apply a multilocus approach and global sampling strategy to better resolve the taxonomy and evolutionary history of this important fungal genus.