Using ITS nrDNA sequence data, the Caloplaca cerina group (Teloschistaceae) is defined here as a monophyletic, but internally richly branched lineage. The group is also characterized by a combination of morphological and anatomical characters. Its internal lineages are supported by phenotypic characters in addition to ecology and distribution. Within the large C. cerina group, we have found at least 20 phylospecies in the temperate zone of the Northern Hemisphere. Two species complexes do not produce any vegetative diaspores: the polyphyletic, corticolous Caloplaca cerina s. lat. (six separated cryptic or semi-cryptic species) and the monophyletic C. stillicidiorum s. lat. that grows mainly on plant debris, small shrubs and bryophytes and consists of at least four internal lineages. All lineages producing vegetative diaspores (soredia, blastidia, isidia or lobules) are phenotypically characteristic and represent fairly easily distinguishable species: C. chlorina, C. isidiigera, C. monacensis, C. subalpina, C. thracopontica, C. turkuensis and C. ulmorum. Only the North American sorediate C. pinicola possibly represents an aggregate of species. Caloplaca sterilis is described as a new species. A key to the phenotypically distinguishable species is provided.
Lectotypes are designated for C. albolutea, Caloplaca cerina f. coronulata and for C. monacensis. The Australian C. hanneshertelii belongs to this group, but this and other possible species from the Southern Hemisphere are not treated here in detail. Some species traditionally placed in the C. cerina group due to their similar morphology are excluded here on the basis of our phenotype examinations and molecular data. Caloplaca albolutea, C. mydalaea and C. virescens are uncertain taxa and their identities still remain unclear.