Arthonia parietinaria - A common but frequently misunderstood lichenicolous fungus on species of the Xanthoria parietina-group.

Arthonia parietinaria is described as new to science. Host of the type and at the same time the only confirmed host species is the foliose macrolichen Xanthoria parietina. Sequence data of nucLSU rRNA genes reveal a close relationship to Arthonia molendoi. A. parietinaria is recorded for many countries in Europe, western Asia, and northern Africa.