Plants: very coarse and stiff, dark green, olive green, or black, all with or without golden green or golden brown mottling. Stems: to 8 cm, denuded proximally or with persistent, shredded bases, unbranched or irregularly branched; hyalodermis absent, epidermal cells small, walls thick, similar to subadjacent cortical cells, central strand well developed. Leaves: stiffly and loosely imbricate to erect-spreading, straight, sometimes secund, shrinking and twisting when dry, spreading when moist, usually broadly ovate, elliptic, or orbicular, sometimes ovate, transverse, or triangular, plane or shallowly concave, (0.6–)0.8–1.2(–1.5) × (0.4–)0.6–1.2(–1.4) mm; margins plane, entire or weakly denticulate; apex usually obtuse or rounded; costa stout, single to 3/4 leaf length, often 2-fid, occasionally double and short; alar cells few, quadrate to rectangular, region not clearly differentiated; basal laminal cells usually longer, wider than medial cells, walls more incrassate, yellowing; medial cells rhomboid, fusiform to short-fusiform, or linear-flexuose, 22–48(–64) × (4–)5–7(–10) µm; apical cells rhombic or rounded; marginal cells often in ill-defined border of short cells. Sexual: condition autoicous; perigonia and perichaetia not in bracted complex; perichaetial inner leaves lanceolate, plicate, margins recurved, entire, teeth few or absent at apex, apex acute or obtuse, costa single, strong. Seta: red or brown, 0.8–1.7 cm. Capsule: with endostome cilia 1–3.
Irrigated to emergent acidic rock in montane streams, rock, wood, in slow moving water or ponds. moderate to high elevations (500-3100 m). Greenland, Alta., B.C., Nfld. and Labr., N.S., Que., Alaska, Calif., Colo., Mont., Wash., Europe, Atlantic Islands (Iceland).
Hygrohypnum smithii is a well-defined species, easily recognizable by the coarse, rigid habit, usually broadly ovate to orbicular leaves, and stout, usually single costa. The alar cells have incrassate, yellowing walls.