Zwackhiomyces turcicus is described as new from the thallus of Physcia magnussonii from southern Turkey. The new species produces one of the largest ascomata in the genus and is easily differentiated from Z. physciicola (described from Physcia caesia) by its larger verruculose ascospores and thinner interascal filaments. Key words — biodiversity, lichenicolous fungi, lichens.