Two new European species from the heterogeneous Caloplaca holocarpa group (Teloschistaceae)

The Caloplaca holocarpa group contains members of the family Teloschistaceae with a strongly reduced thallus and conspicuous yellow, orange or red apothecia. In the absence of well-defined thallus characters, taxa of this group must be identified mainly by apothecial characters and are as a result often difficult to separate. The species of this group have been shown not to form a monophyletic entity, with representatives of other Teloschistaceae with more complex thalli intermixed among them. Caloplaca skii and C. syvashica are recognized here as two homogeneous clades with Caloplaca holocarpa-like phenotypes. Caloplaca skii, which is widespread in southern Europe, resembles C. cerinelloides but is distinguished by its smaller and narrower ascospores and by growing predominantly on xerophilous shrubs. Caloplaca syvashica is restricted to shrubs in salt marshes in the northern Black Sea region. It is similar to the British Caloplaca suaedae and Australian C. yarraensis, but differs from both, mainly in ascospore characters. Caloplaca yarraensis is closely related to the new C. syvashica but arguments against their conspecificity are emphasised. A key for epiphytic C. holocarpa-like Teloschistaceae from Europe is provided.