Plants bright green, somewhat glaucous, becoming reddish brown with age. Stems 1--2.5(--3) cm. Leaves 2.5--5 mm, lanceolate from a weakly sheathing base, broadly incurved and subtubulose when dry, somewhat spreading but remaining incurved and strongly channeled distally when moist; margins entire to finely and distantly serrulate; costa percurrent or shortly excurrent as a short mucro, the adaxial surface with several low continuous or interrupted abaxial lamellae; abaxial surface of lamina smooth or sporadically with scattered short lamellae near the apex of leaf; adaxial lamellae 8--20, 6--13 cells high, restricted to the costa, crispate-undulate, extending to the middle of the leaf or below, the margins finely and irregularly crenulate with bulging marginal cells, smooth; median cells of lamina 15--20 µm, somewhat smaller towards the margins, rounded subquadrate, thick-walled; marginal teeth distant, minute, unicellular; perichaetial leaves 3--3.5 mm, narrowly lanceolate. Seta stout, pale brown, 2--4 cm. Capsule 2--4 mm, cylindric, slightly larger at the base, terete or irregularly angled or ridged; peristome teeth 32, double, somewhat irregular. Spores 10--15 µm.

Soil, gravel, and moist peaty embankments, open disturbed sites, roadcuts, beside paths, on lake shores, stream banks, late snow areas, also aquatic in rapidly flowing glacier melt streams; 500--2200 m; Greenland; Alta., B.C., Nfld., N.S., Yukon; Alaska (including Aleutians), Mont., Oreg., Wash.; Europe (southward to Spain and Turkey); Asia (Japan).

An Arctic-alpine species widespread in northern latitudes, O. hercynicum is a pioneer species, typically forming bright green patches on disturbed soil, but like O. falcatum, also in aquatic habitats.