A revision of the genus Psathyrella, with a focus on subsection Spadiceogriseae

Specimens belonging to taxa traditionally assigned to the subsection Spadiceogriseae of the genus Psathyrella were analyzed both morphologically and molecularly. Samples included mainly European collections, selected GenBank accessions, and specimens of various North American taxa described by Smith (1972) and deposited at the Herbarium of the University of Michigan (MICH). Three additional taxa from Africa and Central America were also included. Bayesian and Maximum Likelihood analyses of two loci (ITS and Tef-1α) independently and together supported the monophyletic nature of the subsection Spadiceogriseae, and identified nine statistically supported clades within the subsection. North American and European species often fell within the same clade, suggesting a relatively recent origin of the subsection or human induced intercontinental movement. While this study determines for the first time that the presence of a white veil is diagnostic for the entire subsection, very few morphological traits were associated with individual clades, but clades were often distinctively different in terms of habitat association, suggesting that trophic interactions may have driven the evolution of this group of fungi. Combined, morphological and DNA analyses revealed both expected and unexpected synonymies. The new combinations P. vesiculosa, P. ochrofulva and P. sanjuanensis are proposed, and the new species P. rogersiae is described. New information is provided on the taxonomic status and distribution of several species including P. agrariella, P. albescens, P. atrifolia, P. bivelata, P. fatua, P. kauffmanii, P. aff. kauffmanii, P. incondita, P. infida, P. nitens, P. niveobadia, P. phegophila, P. pseudocorrugis sensu Kits van Waveren, P. subnuda. In total, 13 synonymies were proposed. Based on DNA data, five species of uncertain validity were confirmed as valid, while six species may be ambiguous and may require an in-depth re-analysis. The information gathered in this study was used to generate a key to the species of the subsection Spadiceogriseae.