Hygrophorus roseodiscoideus Bon & Chevassut: epitypification and updated biogeography of a poorly known but widespread thermophilous species

Hygrophorus roseodiscoideus Bon & Chevassut is a poorly known species so far reported from Mediterranean Quercus ecosystems of western Europe. The lack of reference sequences for this species hampers its reliable identification by mycologists and fungal ecologists in the DNA era. We here fix this issue by epitypifying H. roseodiscoideus with a sequenced collection from the Aix-en-Provence area, where the species has been described from. We also report several sequenced collections from central European countries and Lebanon, that considerably extend the species’ biogeographical distribution. Based on our findings, H. roseodiscoideus can be characterized as a morphologically distinct thermophilous species, associated with oaks on calcareous soils, distributed along the northern coasts of the Mediterranean, from Spain to the Levant, but also colonizing the warmest Quercus woodlands of central Europe.