Stems (2--)4--6(--10) cm, simple to fasciculately branched. Leaves(4--)5--8 mm, coarsely toothed. Capsule 3--5 × 0.8--1 mm, short cylindric to long-cylindric and subarcuate.

Soil or humus, shaded non-calcareous rock outcrops, banks, and other shady situations; middle to upper elevations; Greenland, B.C., N.B., N.W.T., N.S., Nunavut (Bathurst Is., Ellesmere Is.), Ont., Que., Yukon; Alaska (including the Aleutians), Calif., Colo., Idaho, Maine, Mass., Mich., Minn., Mont., N.H., N.Mex., N.Y., N.C., Oreg., Pa., Vt., Wash., W.Va., Wis.; Mexico; temperate s South America, Europe (s to Turkey); n and c Asia (including Japan, New Guinea), s Africa, Pacific Islands (New Zealand); Australia; Antarctica.

The typical variety is widely distributed across the northern U.S. and Canada, growing in thick masses in crevices and ledges on moist, shaded rock outcrops, also common at all elevations in the Arctic, on tussocks in open tundra, stony banks, and outcrop ledges. Polytrichum var. arcticum has traditionally been the repository for plants with cylindric capsules (as opposed to the smaller, ovoid capsules of var. septentrionale) and probably comes closest to being “typical” P. alpinum. The common expression of P. alpinum in eastern N. Am. has a distinctive aspect, tall and gracile, with slender, subtubulose leaves, and elongate, slender, distinctly curved and inclined capsules (G. E. Nichols 1937), and has no exact counterpart among the traditionally recognized varieties of the species. The var. brevifolium has a more northerly distribution and is smaller in all its parts, but has the toothed leaves and cylindric capsule of the typical form.