Description and distribution of new for Russia species Endocarpon crystallinum J.C. Wei et Jun Yang, known from the deserts of North China and found on the western coast of Baikal Lake in steppe ecotopes on calcareous soil in crevices of limestone rocks and among stones are reported. The species is characterized by a thick epinecral layer, which looks like big whitish pyramidal crystals, maintaining a lamellar, cellular structure, formed by necrotic cortical cells with thick walls; by thick exciple, light in the inner part and brown-black in the outer part; by the absence of true lower cortex, but by the presence of a layer of closely parked spherical medullary cells with brown-black pigmented walls, and by the presence of brown-black rhizohyphal prothallus (weft) and rhizohyphal bundles (not true rhizines). Several rare species, Heppia echinulata Marton et Galun, H. solorinoides (Nyl.) Nyl., Psora indigirkae Timdal et Zurb., Toninia lutosa (Ach.) Timdal, Solorinella asteriscus Anzi and others inhabit together with Endocarpon crystallinum the same ecotopes.Key words: lichens, Endocarpon crystallinum, rare species, steppe ecotopes, Priolkhonie.