Fifty-six known lichenicolous, non-lichenized Opegrapha (Roccellaceae, Arthoniales) species (containing some undescribed taxa) are listed here, five of which are known from Caloplaca (Teloschistaceae, Teloschistales). Opegrapha vulpina, a new lichenicolous fungus on endolithic Caloplaca subg. Pyrenodesmia (Caloplaca erodens and rarely C. albopruinosa), is described from Europe. A second new species, Opegrapha hellespontica, lichenicolous on Caloplaca aurantia, is described from the European part of Turkey. Two possible sibling species of Opegrapha rupestris s. l. lichenicolous on Caloplaca cirrochroa and C. variabilis s. l., respectively, are discussed in the paper, but have not been described.
