Plants 1--2.5 cm. Stem leaves erect-appressed when dry, ovate-lanceolate to narrowly lanceolate, 2.5--4.5 mm, gradually narrowed to acuminate-cuspidate apex; margins recurved-revolute to near apex, entire; distal laminal cells 9--13 µm wide, 1-stratose, with 1--3 low, forked papillae; basal laminal cells elongate-rectangular, nodose. Sexual condition goniautoicous. Seta 0.5--1.1 mm. Capsule 1/2 emergent when dry, barely emergent when moist; urn ovate-oblong when mature, oblong to oblong-cylindric and constricted beneath mouth when old and dry, 1.6--2.4 mm, strongly 8-ribbed 1/2 to 2/3 the length; stomates superficial; peristome double; endostome segments 16, large, coarsely papillose; exostome teeth 8, reflexed-recurved, finely papillose, sometimes papillose-striate below. Calyptra short-conic, hairy, hairs with small papillae. Spores 12--18 µm.

Rocks, rarely lava, dry montane areas; middle elevations; Calif., Nev., Wyo., Wash. Restricted to w North America.

This rare species has been collected only a few times. Orthotrichum praemorsum is distinguished from other species by strongly-ribbed, emergent capsule and by the cuspidate, shortly hyaline-tipped leaves.