Cortinarius subgenus Myxacium section Colliniti (Agaricales) in Fennoscandia, with special emphasis on the Arctic-alpine zones

Abstract The taxonomy and ecology of Cortinarius subgenus Myxacium section Colliniti in Fennoscandia is treated. Most species of this group have their optima in oligotrophic habitats, and play an important role in upper boreal and Arctic-alpine regions. Variation in spore morphology is subjected to numerical treatment. Relevant nomenclatural types and protologues for classical names are examined. Presence of clamp connections is stated to be an important diagnostic character towards the most closely related section, Defibulati. Also, SEM pictures have revealed a significant difference in the spore ornamentation between the two groups. Spore shape and size provide important diagnostic characters for separation of the different taxa of section Colliniti, as shown by scattergrams. The most distinctive species in this respect are found to be C. mucosus, with characteristically narrow spores, and C. collinitus with larger spores. The species concept within the group is discussed. Seven Fennoscandian species are recognized and their taxonomy and ecology are discussed. C. septentrionalis (type from Norway) and C. fennoscandicus (type from Finland) are described as new. Both species are common in upper (northern) boreal mountain birch (Betula) woodlands and under the low shrub Betula nana in the low alpine and arctic zones. The status of Agaricus collinitus Sow: Fries is discussed in more detail.