Systematic analysis of Russula in the North American Rocky Mountain alpine zone

Abstract

Russula Pers. (Russulales) is an important ectomycorrhizal fungal genus in alpine and Arctic regions where it occurs in association with Salix, Betula, Dryas, and Polygonum. Despite Russula’s importance and abundance in Arctic and alpine systems there has been no in-depth systematic analysis of the genus in these habitats. This is also true for alpine areas of the Rocky Mountains where only four species of Russula have been casually reported above treeline. The genus Russula is large, diverse, and intraspecific morphological variation makes taxonomic classification difficult, which means verification using molecular techniques is necessary. This research compared Rocky Mountain alpine Russula collections to Arctic and alpine collections from Europe using an in-depth morphological study and a systematic molecular analysis of the nuc rDNA ITS1-5.8S-ITS2 region (ITS barcode) and the second largest subunit of the RNA polymerase II gene (RPB2). Over 130 Russula collections were sequenced including type material. This research confirmed eight species with intercontinental distributions in Arctic and alpine habitats, including R. nana, R. laccata, R. subrubens, R. cf. pascua, R. heterochroa, R. saliceticola, R. purpureofusca, and R. laevis. Two species are reported from subalpine habitats at treeline; R. montana with conifers and R. altaica with Betula. The Russula present in the Rocky Mountain alpine represent a subset of those known from other Arctic-alpine habitats and data show that multiple Russula species independently colonized alpine habitats. This is the first formal report of R. altaica, R. saliceticola, and R. subrubens in the Rocky Mountains and of R. heterochroa and R. purpureofusca in North America. Previous work matched sequences extracted from ectomycorrhiza in Canada to R. laevis, but this is the first work to collect this species and report it in North America. A key for the identification of alpine Russula in North America is provided. A history of Arctic and alpine mycology in North America is included and provides background material for the study. This work contributes to our knowledge of biodiversity in Arctic and alpine systems and will promote future ecological and taxonomic research on alpine Russula because little is known about these species or how to identify them.