The worldwide rare Iwatsukia jishibae (Steph.) Kitagawa was found to be relatively common in Khamar-Daban Range near the south end of Lake Baikal (South Siberia). A detailed description of this species, as well as differences from allied species are given, and there is a key to genera of Cephaloziaceae in Russia. Mainly a tropical-subtropical species, I. jishibae has a disjunct distribution in Central America, West and East Africa, Indian Ocean islands, Papua-New Guinea, Nepal, Japan, Korea and South Siberia. This species occurs exclusively on rotting wood. Iwatsukia exigua is believed to be conspecific with I. jishibae.