Placopyrenium ariyanense from northeastern Iran is described as new to science. It is characterized by a small, areolate thallus, grey pruinose, black-rimmed areoles, a granule-inspersed, but not chalky medulla, and simple ascospores, which are broader than those in P. iranicum. It is probably a juvenile parasite on crustose lichens. Key words: Pyrenocarpous lichens, fungi, taxonomy.