The nomenclature and taxonomy of Acarospora molybdina is revised using morphological and molecular data. The new combination Myriospora molybdina is proposed and Acarospora hysgina is recognized as a distinct species while A. brunneola is reduced to synonymy with A. hysgina. In its new circumscription M. molybdina is an arctic species, in Scandinavia only occurring in northernmost Norway. Further localities are reported from Greenland, Russia, Svalbard and the USA (Alaska). Acarospora hysgina is the correct name for a species distributed along the west coast of Sweden and Norway, formerly thought to belong to A. molybdina. Localities are also reported from Canada (New Brunswick), Greenland and the USA (Maine). The following names are lectotypified: Acarospora brunneola, A. molybdina var. confusa, Lecanora ereutica ? microcyclos, Parmelia ereutica, P. hysgina and P. molybdina. Acarosporaceae, beta-tubulin, ITS, Lecanoromycetes, lichens, mrSSU, phylogeny