New species of Cortinariussect. Austroamericani, sect. nov., from South American Nothofagaceae forests

ABSTRACTIn this study, we document and describe the new Cortinariussection Austroamericani. Our results reveal high species diversity within this clade, with a total of 12 recognized species. Of these, only C. rufuswas previously documented. Seven species are described as new based on basidiomata collections. The four remaining species are only known from environmental sequences. All examined species form ectomycorrhizal associations with species of Nothofagaceae and are currently only known from Argentinean and Chilean Patagonia. The phylogenetic analysis based on the nuc rDNA internal transcriber spacer (ITS1-5.8S-ITS2 = ITS) and partial 28S gene (28S) sequences shows that this section is related to other taxa from the Southern Hemisphere. Species in this group do not belong to subg. Telamonia, where C. rufuswas initially placed. Cortinarius rufusand the newly described C. subrufusform a basal clade within sect. Austroamericanithat has a weakly supported relationship with the core clade. Because the two species are morphologically similar to species from the core clade and share their distribution and Nothofagaceae associations, we include them here as part of sect. Austroamericanisensu lato (s.l.) until more material is available to refine the delimitation.