In the Patagonian region, Cortinarius is the most diverse and abundant genus of ectomycorrhizal fungi with at least 250 species. Sequestrate forms were until recently documented within the genus Thaxterogaster, a genus now known to be polyphyletic, and many were consequently transferred to Cortinarius. Original descriptions were mostly available in German and Spanish and interpretations of morphological structures outdated. Despite recent advances in Cortinarius systematics, the current classification, diversity, and ecology of sequestrate “cortinarioid” fungi in Patagonia remain unclear. The objective of this study was to provide an update on sequestrate Cortinarius of southern South America. We documented each species with morphological descriptions, photographs, basidiospore scanning electron microscopy (SEM) images, and molecular characterization using nuc rDNA internal transcribed spacer region ITS1-5.8S-ITS2 (ITS) and nuc 28S rDNA (28S) sequence data. Original descriptions of taxa were also translated to English and revised based on fresh collections. We documented 24 species from Patagonia based on molecular data and conducted morphological and phylogenetic analysis for 18 previously described species based on type and reference specimens. In addition, we formally described two new species. Four additional taxa were provisionally determined as new but require further study. New ITS sequence data were produced from eight type specimens. We also provide a new name, Cortinarius gloiodes, nom. nov., for the taxon previously described as Thaxterogaster gliocyclus. In addition to the species treated in detail, we provided additional reference information and discussion on six described species that remained incompletely known or for which no recent collections were found. Of the 24 taxa documented from Patagonia, 15 species were assigned to 12 current sections in the genus Cortinarius. Analysis of spore ultrastructure showed that sequestrate forms of Patagonian Cortinarius lack a true perisporium.

Sequestrate fungi have enclosed hypogeous, subhypogeous, or epigeous basidiomes and have lost the ability to actively discharge their spores. They can be distinguished as gasteroid (basidiome fully enclosed with a loculated hymenophore) or secotioid (basidiome with some agaricoid or pileate-stipitate features, but the lamellae are misshapen and unexposed or mostly unexposed at maturity). There are only four reports of sequestrate taxa within the ectomycorrhizal family Inocybaceae, three from Australia and one from western North America. Recent field work in Nothofagaceae forests in the Chilean coastal range revealed novel sequestrate forms of Inocybe. We examined specimens using a combination of morphological and molecular data from nuc rDNA internal transcribed spacer region ITS1-5.8S-ITS2 (ITS) and portions of nuc 28S rDNA (28S) and the gene encoding the second largest subunit of RNA polymerase II (rpb2). Here, we describe four new sequestrate Inocybe species, I. ranunculiformis, I. anfractuosa, I. illariae, and I. nahuelbutensis. Results of our phylogenetic analysis resolved the four new species as distinct species-level clades with strong support, suggesting that these fungi have convergently evolved sequestrate forms independently. The species described here were all placed along with members of the “smooth-spored temperate austral clade,” which includes almost exclusively Australasian and South American species of Inocybe.

Patagonian collections of the corticioid genus Tomentellopsis have been treated in the past as T. echinospora, a common northern hemisphere species. New collections with DNA sequence data are distinct from the northern hemisphere taxon and must be considered a different species, endemic to the temperate subantarctic forests of Patagonia. We use molecular and morphological methodologies to study this new corticioid fungus and describe it as Tomentellopsis rosannae sp. nov.