Cortinarius subgenus Leprocybe, unexpected diversity and significant differences in species compositions between western and eastern North America.

The focus of this paper is the North American species of in subg. . Eighteen species, including twelve new ones, and two tentative (aff.) species, are delimited based on morphological and molecular data (DNA ITS-LSU sequences). Existing type specimens of species in subg. were also studied, and neo- or epitypes designated for , , and to stabilize the nomenclature. In addition, to improve the infrasubgeneric classification of three new sections are proposed: sect. , sect. and sect. . This study adds substantial information to the knowledge of subg. in North America against a background of European species. To date only two species, and have been reported from both continents.