Morphological differences between two arcto-alpine species of Oligotrichum, O. hercynicum and O. falcatum (Polytrichaceae) are rather few, overlapping and not always expressed, thus problems with their distribution in Asia remain. In the present study we found that morphology of these species corresponds well with the six characteristic substitutions in nrITS1, providing more robust ground for delimitation of these two species. Oligotrichum hercynicum occurs in relatively oceanic climates in Northern Europe, mountains of Central Europe, Caucasus, Kuznetskij Alatau in South Siberia, Kamchatka, Chukotka, and northern North America. Contrary to that, Oligotrichum falcatum has the Beringian distribution, in a broad sense. It is known from mountains of South Siberia (westwards to Altai), Yakutia, xeric regions of North-East Asia and Arctic North America, including Western Greenland, and also reported from Tibet.