Stems to 2 cm, slender and wiry, in dense tufts. Leaves densely imbricate, channeled and incurved when dry, scarcely spreading when moist; sheath broadly elliptic; marginal lamina typically entire, or finely and remotely serrate toward the tip. Capsule small and subglobose.

On soil at higher latitudes and elevations; Alta., Nfld. & Labr. (Labr.), Man., N.W.T., Nunavut, N.S., Que.; Calif., Colo., Mont., Utah, Wyo., Wash.; Europe, n. Asia.

Polytrichastrum alpinum var. septentrionale is an Arctic-alpine plant. In Arctic North America there is a correlation between capsule shape and leaf serration, plants with distinctly serrate leaves having ovoid-cylindric or cylindric capsules, whilst those with entire or subentire margins have subglobose or ovoid capsules (D. G. Long 1985).