Stems 1--2 cm, in compact tufts. Leaves fragile, constricted at the junction of sheath and blade, the blade caducous; marginal lamina entire, rarely distantly serrulate. Capsule ovoid or subglobose.

Growing where subject to periodic inundation, wet meadows, springs and lake margins, occasional in open tundra, beach ridges and roadside banks, at lower elevations. Greenland; N.W.T., Nunavut (Baffin Is., Ellesmere Is., Melville Is.), Arctic Alaska; Europe (n Scandinavia); Asia (Russia in Siberia).

Polytrichastrum alpinum var. fragile is a distinctive plant of the high Arctic with regularly caducous leaves, in N. Am. common only in arctic Alaska on the coastal plain to 100(--800) m, with scattered records throughout arctic Canada (D. G. Long 1985).