Plants usually green-, red- or dark-brown. Stems to 0.6 cm, central strand present. Stem leaves appressed-incurved when dry, weakly spreading and not keeled when moist, monomorphic, ovate-lanceolate, broadly concave adaxially across leaf, usually 0.7--1.2 mm, base weakly differentiated in shape, ovate, margins weakly recurved at midleaf, minutely crenulate, apex rounded-acute, often weakly cucullate; costa ending (2--)4--6 cells below the apex, not strongly spurred, little tapering, without an adaxial pad of cells, adaxial costal cells quadrate or short- to long-rectangular, 2 cells wide at midleaf often grading to 4 below, guide cells in 1 layer; basal laminal cells differentiated medially, walls thin or thick, quadrate to rectangular, not perforated; distal laminal cells 9--11 wide, 1:1, papillae absent visible or low, simple, 1 over each lumen, lumens sub-quadrate to irregular, walls evenly thickened, weakly convex on both sides of lamina, 1-stratose. Specialized asexual reproduction by mostly unicellular gemmae in leaf axils. Sexual condition only perichaetial plants seen. Sporophyte unknown,. Distal laminal KOH reaction red.

Calcareous rock or soil, bluffs, often near waterfalls; 100--3000 m; N.W.T., Yukon; e Asia.

An extremely rare species known from only two stations in the range of the flora: N.W.T.: Mackenzie Distr., Nahanni National Park, Virginia Falls, Scotter 22433 (NY), and Yukon: Firth R. basin, near mouth of Mancha Creek, 68°40'N, 141°W, Sharp MC-58152a p.p., 1958 (NY). Didymodon perobtusus has several characters in common with D. revolutus of the southwestern U. S. A. and Mexico, including leaf and laminal papillae shape and unicellular gemmae borne in dense axillary clusters; however, D. revolutus differs by the strongly recurved to revolute margins, leaf cells with thin, light yellow walls, and gemmiferous plants uncommon, the propagula all unicellular. Both North American collections seen were from stations in which D. subandreaeoides is also present, growing in separate or occasionally confluent cushions. The taxonomic position of D. perobtusus is not clear. It is placed near D. subandreaeoides because of dark, reddish color, and similarity of areolation and laminal papillae. It may, however, turn out to be related to D. tophaceus, with which it has a certain resemblance.