Phylogeny, morphology, and ecology resurrect previously synonymized species of North American Stereum

Abstract

ABSTRACTStereum is a globally widespread genus of basidiomycete fungi with conspicuous shelf-like fruiting bodies. Several species have been extensively studied as pathogens and for medically relevant secondary metabolites, but prior to this publication the molecular phylogeny of Stereum had not been analyzed, despite 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 nuc rDNA ITS1-5.8S-ITS2 (ITS barcode) 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 or confused for S. ostrea: Stereum fasciatum, Stereum lobatum, and Stereum subtomentosum. Stereum hirsutum ITS sequences taken from GenBank suggest that other Stereum species may also 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.