Plants in usually rounded cushions, green to blackish. Stems 1--2 cm, central strand present. Stem leaves incurved and moderately contorted when dry, spreading when moist, oblong- to linear-lanceolate, tapering to a slender and acuminate, often hyaline apex, 2.5--4.5 × 0.3--0.5 mm. keeled, margins plane or recurved below on one side, awns short, often only a hyaline point, occasionally long and denticulate, costa projecting on dorsal side; distal laminal cells 1-stratose, margins and apex 2-stratose; medial laminal cells rectangular, nodulose, thick-walled; basal juxtacostal laminal cells elongate, slightly sinuose, thick-walled; basal marginal laminal cells elongate, thin-walled. Gemmae absent. Sexual condition autoicous or dioicous. Seta arcuate, 1.5--2 mm. Capsule occasionally present, emergent to exserted, yellowish, obloid, smooth or somewhat wrinkled when dry, exothecial cells thin-walled, annulus present, operculum conic to rostrate, peristome teeth orange, divided distally, papillose. Calyptra mitrate.

Shaded damp, acidic rock; 500--2500 m; Alta., B.C., Labr., N.B., Yukon; Calif., Colo., Maine, N.H., N.Y, Oreg., S.Dak.; Africa (Rwanda, Tanzania, Uganda); Eurasia.

The peculiar east-west disjunct distribution of Grimmia incurva in North America may reflect its preference for damp sites. Specimens have been collected in the New England states and in the Maritime provinces of Canada, with a second widespread area running from the Yukon south through to California. It is uncommon in the continental interior. Grimmia incurva is a skiophilous montane species, characterized by rounded dark-green cushions with linear, slightly contorted leaves, the awns are only visible with a hand-lens. This species has a habit more like Dicranoweisia crispula than a Grimmia. A. J. Grout (1933) did not observe anything striking about G. incurva, noting only that in North America the species occurs from British Columbia to California, and that it seldom fruits. H. A. Crum and L. E. Anderson (1981) reported immersed capsules, but that is not correct; they are clearly exserted (H. C. Greven 1995). H. A. Crum and L. E. Anderson (1981) also observed that: "Specimens recorded from Maine can be considered as a shade form of G. donniana." The problem, however, is widespread. H. C. Greven found that nearly all G. incurva specimens from New York and New Hampshire in MICH were misidentified as G. donniana; many of them richly fruiting, and cladautoicous with small inconspicious androecia, more rarely gonioautoicous. Grimmia donniana is known for its autoicous character and is usually found with capsules, these characters being the most likely reasons for the misidentification. Grimmia donniana and G. incurva also share pale capsules and a comparable areolation with conspicuous hyaline, straight-walled basal cells sharply contrasting with sinuose mid leaf cells. However, in G. incurva, the leaves are linear and more or less crisped and contorted when dry, while in G. donniana the leaves are elongate-lanceolate, imbricate and slightly curved when dry.