Plants in compact, dark green tufts. Stems 1--3(--5) cm. Leaves erect-spreading, lanceolate, subulate, 2--3 mm; costa 30--55 µm wide at base, short-excurrent, rough near tip; distal laminal cells mostly subquadrate (1--2:1), incrassate; basal laminal cells elongate, alar cells differentiated, quadrate or slightly enlarged. Seta 4--6(--8) mm. Capsule exserted, slightly curved, obscurely to distinctly ribbed when dry, annulus developed, separating; peristome large, not spreading outward when dry. Spores 18--30 µm.

Capsules mature summer. Siliceous rock or soil; high-alpine elevations; Greenland; Nfld., N.S., Que.; Oreg.; Europe.

This rare Arctic-alpine moss is found on rock ledges or crevices at high elevations. It is distinguished from other species of Arctoa by its short-excurrent costa, shorter seta (the length is highly variable), and peristome not spreading when dry.