Exidia and Exidiopsis (Auriculariales, Basidiomycota): a reconsideration

The taxonomy of the Auriculariaceae (Auriculariales, Basidiomycota) is revised based on morphological data and four- and three-marker datasets, with special emphasis on the Exidia clade. We argue in favor of retaining Exidia as a large genus, encompassing most species previously relegated to it, with an addition of four effused (Exidiopsis-like) species. Phylogenetic data allow us to justify two segregates from Exidia s. lato, namely the reinstated Ulocolla (Exidia saccharina complex) and a newly erected genus Descidia, encompassing Exidia repanda and E. thuretiana. At large, morphological data corroborate this splitting. Exidiopsis effusa, the generic type of Exidiopsis, is typified and redescribed; together with a newly described E. perflua, it constitutes the genus Exidiopsis s. str. The rest of Exidiopsis s. lato species studied by us are redistributed among the redefined genera Adustochaete, Leiostroma, Proterochaete, and Ulocolla, as well as a newly introduced genus, Tegmenticium. Amphistereum is placed among the synonyms of Eichleriella and the single representative of Sclerotrema, Exidiopsis griseobrunnea, is moved into Ulocolla. In total, 52 species are properly redescribed or introduced below, of them twenty are new to science, and twenty new combinations are proposed. Additionally, we detected two single-species lineages: Pholiobasidion senex gen. nov. et sp. nov., from North America, which is recovered as the sister group to all other members of the Auriculariaceae sampled, and Scrupulispora perparvula gen. nov. et sp. nov., from Europe.