Plants: to 12 cm, soft. Stems: 1–3 mm wide across leafy stem, irregularly branched to loosely 1-pinnate, not frondose or bushy, branches turgid, innovations inconspicuous. Stem: leaves erect to erect-spreading, loosely imbricate, becoming more tightly imbricate toward stem apices, ovate to elliptic-ovate, somewhat concave, 1.5–2.5 × 1–1.4 mm; margins serrulate to nearly entire proximally, serrate distally; apex abruptly narrowed; costa single; medial laminal cells 30–60 × 5–7 µm. Branch: leaves imbricate, ovate-lanceolate to lanceolate, 1.3–2 × 0.4–0.9 mm; costa single. Seta: 1–3 cm. Capsule: ovoid, 1.3–1.8 mm.
Soil, humus, old logs, rock in moist forests, rarely fens, and tundra, often along streams or beside waterfalls. low to high elevations (0-3000 m). Greenland, Alta., B.C., N.B., Nfld. and Labr., N.W.T., N.S., Ont., Que., Yukon, Alaska, Colo., Maine, Mich., Minn., N.H., N.Y., Vt., Wash., Wis., Eurasia.
Hylocomiastrum pyrenaicum may be more common in calcareous regions.