Plants light green to dark brownish green, dull, in loose tufts. Stems 1-6(-18) cm, tomen-tose to scarcely tomentose with white or reddish brown rhizoids. Leaves falcate-secund, often strongly so, sometimes somewhat sparse, distal leaves curled, proximal leaves with flexuose apices, slightly to strongly curled and crisped when dry, smooth, (3-)4-7(-10) × 0.6-1 mm, concave below, keeled above, from a lanceolate base to a gradually narrowed, fine, keeled subula; margins entire proximally, serrulate to strongly serrate in the distal half, sometimes nearly entire throughout; laminae 1-stratose and usually 2-stratose above on one or both margins, rarely some 2-stratose regions near costa; costa excurrent, 1/6-1/4 the width of the leaves at base, strong, terete, papillose to spinose distally on abaxial surface, occasionally almost smooth, sometimes extending to costa, abaxial ridges absent, with a row of guide cells, 2 well-developed stereid bands extending to distal part of leaf, adaxial epidermal layer of cells not differentiated, abaxial epidermal layer differentiated; cell walls between lamina cells slightly bulging; leaf cells smooth to slightly papillose below on abaxial surface, papillose to spinose prorate above on abaxial surface; alar cells 2-stratose, strongly differentiated, sometimes extending to costa; proximal laminal cells elongate, pitted, (19-)43-62(-93) × (2-)6-8(-12) µm; distal laminal cells irregularly rounded, elliptic, short-rectangular to quadrate, not pitted, (7-)9-23(-36) × (4-)8-12(-14) µm. Sexual condition dioicous; male plants as large as females, growing intermixed, or in separate patches; interior perichaetial leaves abruptly short-acuminate, convolute-sheathing. Seta 1-3.5 cm, solitary, yellow, reddish yellow or brown. Capsule 1-3 mm, arcuate, inclined to horizontal, strumose, strongly furrowed when dry, somewhat contracted below mouth, dark brown to reddish brown; operculum 1-2 mm. Spores 14-24 µm.
Varieties ca. 7 (2 in the flora): North America, Europe, Asia.