Cleistocybe, a new genus of Agaricales

A new clitocyboid genus of Agaricales, Cleistocybe, is described to accommodate the isolated evolutionary position of the new species Cleistocybe vernalis inferred by a previously published multigene phylogenetic study. Cleistocybe is distinguished from other clitocyboid lineages by a combination of morphological characters, including lamellae that become gray in age, an interwoven hymenophoral trama with divergent elements when young, strongly interwoven pileipellis with pigmented and encrusted hyphae, white spore deposit, a distinct or ephemeral fibrillose to submembranous partial veil, and smooth, inamyloid basidiospores that are inequilateral in profile view. Cleistocybe encompasses two species, C. vernalis and Clitocybe gomphidioides, based on morphological comparisons with C. vernalis. Clitocybe subvelosa is confirmed as conspecific with C. gomphidioides based on morphological and ITS sequence comparisons of type collections. Cleistocybe is known only from western North America in coniferous forests and appears most closely related to the ectomycorrhizal genus Catathelasma and the saprotrophic genera Callistosporium, Macrocybe, and Pleurocollybia based on nLSU-rDNA phylogenetic analysis. Together these lineages constitute the Catathelasma clade.