Orthotrichum affine subsp. praemorsum (Venturi) Kindberg; O. arcticum var. praemorsum (Venturi) Wijk & Margadant; O. microblephare var. praemorsum (Venturi) Grout

Plants 1-2.5 cm. Stem leaves erect-appressed when dry, ovate-lanceolate to narrowly lanceolate, 2.5-4.5 mm; margins recurved-revolute to near apex, entire; apex gradually acuminate-cuspidate; basal laminal cells elongate-rectangular, walls thick, nodose; distal cells 9-13 µm, 1-stratose, papillae 1-3 per cell, 2-fid, lo w. Specialized asexual reproduction absent. Sexual condition gonioautoicous. Seta 0.5-1.1 mm. Capsule 1/2 emergent when dry, barely emergent when moist, ovate-oblong when mature, oblong to oblong-cylindric when old, 1.6-2.4 mm, strongly 8-ribbed 1/2-2/3 capsule length, constricted below mouth when dry; stomata superficial; peristome double; prostome absent; exostome teeth 8, reflexed-recurved, finely papillose, sometimes papillose-striate proximally, ; endostome segments 8, well developed, , of 1 row of cells, coarsely papillose. Calyptra short-conic, smooth, hairy, hairs papillose. Spores 12- 18 µm.

Rock, lava, dry montane areas; of conservation concern; moderate elevations; Calif., Nev., Wash., Wyo.

Orthotrichum praemorsum is rare, known only from a few collections. The species is distinguished by its strongly ribbed, emergent capsules and cuspidate, shortly hyaline-tipped leaves.