Unexpected species diversity and contrasting evolutionary hypotheses in Hebeloma (Agaricales) sections Sinapizantia and Velutipes in Europe

Hebeloma velutipes is one of the most common and abundant members of the ectomycorrhizal basidiomycete genus and H. sinapizans is one of its oldest and most commonly recorded species. Using large sample sizes, several loci and the analysis of types, we explored the taxonomy, species limits, distribution and the infrageneric classification of these two species and their relatives. By relying almost exclusively on sequenced material, we were able to attain a marked refinement of species descriptions. Phylogenetic results are congruent with respect to the delimitation of species, but suggest conflicting evolutionary histories of the species phylogeny. Using multi-species coalescent analysis, phylogenetic support for H. sects. Velutipes and Sinapizantia was assessed, finding clear support for H. sect. Sinapizantia but ambiguous results for H. sect. Velutipes. One species, H. subconcolor, previously accommodated in H. sect. Denudata, is placed in H. sect. Velutipes. Hebeloma bulbiferum, so far not considered in systematic treatments, is shown to belong to H. sect. Sinapizantia. Unexpectedly, H. velutipes turned out to be distinct from H. leucosarx. Hebeloma erebium comb. nov., H. celatum sp. nov. and H. quercetorum, formerly treated as a single species (H. quercetorum), are demonstrated to be three taxa that are clearly distinct in molecular terms, even though, morphologically, they can be deceptively similar; H. erebium and H. quercetorum are, moreover, geographically distinct. The morphological characters used to distinguish the ten recognised European species are outlined. Finally, a lectotype and an epitype are designated for H. sinapizans and a lectotype for H. quercetorum.