As a result of our studies aiming to determine the lichen mycota of the James Ross Island (Antarctic Peninsula), we report Peltigera castanea, a species in the P. didactyla complex from Antarctica and Southern Hemisphere for the first time. Collections were evaluated using morphological, anatomical and molecular characteristics (nrITS). Peltigera castanea has foliose, 4-6 cm lobate thallus; upper surface dark brown to chestnut brown, weakly tomentose (especially in the margins of the lobes) and sorediate. The morphological and ecological variations of this species are discussed in this paper. Key words: Antarctica, first report, lichens, biodiversity, James Ross Island.