Inocybe (Inocybaceae) is one of the most diverse ectomycorrhizal genera in arctic and alpine habitats where the primary hosts are Salix, Betula, and Dryas. Subgenus Inocybe is common in these habitats and typically characterized by the presence of thick-walled pleurocystidia. Here, we focus on species that have angular or nodulose spores. Historically, over 30 taxa from this group have been reported from arctic and alpine habitats. Many names have been synonymized, whereas molecular analysis has revealed new species. Nuc rDNA internal transcribed spacer ITS1-5.8S-ITS2 (ITS) sequence data of 26 type specimens in this group now allow for further taxonomic clarification and comparison across continents of disjunct populations. Here, we compare ITS sequence data and the D1-D2 portion of nuc 28S rDNA (28S) from Rocky Mountain specimens with those of types and European reference material. We report 10 species from the Rocky Mountain alpine zone, all of which are conspecific with known European boreal, montane, or alpine species, and four are described as new; all have intercontinental distributions. Nodulose-spored Inocybe taxa that occur in the Rocky Mountain alpine zone include I. alpinomarginata, sp. nov., I. arctica, I. giacomi, I. leonina, I. murina, sp. nov., I. occulta, I. paragiacomi, sp. nov., I. phaeocystidiosa, I. purpureobadia, and I. subgiacomi, sp. nov. Remarkably, these species occur at elevations up to 4000 m and at latitudes as low as 36°N, hundreds of miles from the Arctic, the European alpine, and original type localities. Distributions are explained in part by host distributions and historical glaciation patterns. A key and full descriptions for Rocky mountain species are provided to promote species recognition.
Keywords: 4 new taxa; Arctic-alpine; Colorado; Inocybaceae; J. Favre; Montana; Salix; biogeography; molecular systematics; taxonomy; type collections.