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 Myriospora molybdina is an arctic species, in Scandinavia only occurring in northernmost Norway. Further localities are reported from Greenland, Russia, Svalbard and the U.S.A (Alaska). Acarospora hysgina is the correct name for populations 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 U.S.A. (Maine). The following names are lectotypified; Acarospora brunneola, Acarospora molybdina var. confusa, Lecanora ereutica β microcyclos, Parmelia ereutica, P. hysgina and P. molybdina.

DNA was extracted from recently collected material or from dried herbarium specimens. Total DNA was extracted using the Qiagen DNEasy Plant Minikit, according to the manufacturer’s instructions. Selected markers for this study were the internal transcribed spacer complete repeat (ITS) and the large subunit of the nuclear ribosomal DNA (nrLSU), the small subunit of the mitochodrial ribosomal DNA (mrSSU), and the coding sequence of the β-tubulin gene (BT). PCR-amplification, purification and sequencing was performed using the same primers and methods as in Westberg et al. (2015, Fung. Diversity 73: 145–158).