Data from: Myriospora molybdina comb. nov. and the identity of Acarospora hysgina

<p>The nomenclature and taxonomy of <em>Acarospora molybdina</em> is revised using morphological and molecular data. The new combination <em>Myriospora molybdina</em> is proposed and <em>Acarospora hysgina</em> is recognized as a distinct species while <em>A. brunneola</em> is reduced to synonymy with <em>A. hysgina</em>. In its new circumscription <em>Myriospora molybdina</em> 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). <em>Acarospora hysgina</em> is the correct name for populations distributed along the west coast of Sweden and Norway, formerly thought to belong to <em>A. molybdina</em>. Localities are also reported from Canada (New Brunswick), Greenland and the U.S.A. (Maine). The following names are lectotypified; <em>Acarospora brunneola</em>, <em>Acarospora</em> <em>molybdina</em> var. <em>confusa</em>, <em>Lecanora</em> <em>ereutica</em> β <em>microcyclos</em>, <em>Parmelia ereutica</em>, <em>P</em>. <em>hysgina</em> and <em>P</em>. <em>molybdina</em>.</p>