Specimens of Caloplaca belonging to the group of C. citrina (Hoffm.) Th. Fr. were collected in different localities in the provinces of Buenos Aires (Argentina) and studied using morphology and nrITS data. They were identified as C. austrocitrina Vondrák, Riha, Arup & Søchting, a species newly described from the Black Sea area, but also found in other European countries. These findings are the first mention of this species for South America and broaden its distribution range considerably. The results also show that the specimens from Argentina are genetically very similar to the European ones and that the variation in this gene within the species seems to be very low.