Authors: Roxanne I. Hastings & Dr. Henk C. Greven

Plants in dense cushions, dark green to almost black. Stems 0.8--1.2(--1.5) cm, central strand present. Stem leaves oblong-lanceolate, 1--2.2 × 0.3--0.6 mm, keeled, not plicate, margin plane, awn 0.3--1.3 mm, costal transverse section prominent, terete; distal laminal cells 2-stratose, not bulging, marginal cells 2-stratose, not bulging; medial laminal cells short-rectangular, sinuose, thick-walled; basal juxtacostal laminal cells long-rectangular, straight, thin-walled (rarely somewhat thick-walled); basal marginal laminal cells long-rectangular, straight, thin-walled, typically hyaline. Perichaetial leaves not enlarged. Sexual condition autoicous. Seta straight, 2--3 mm. Capsule usually abundantly present, exserted, pale yellow-brown, oblong, exothecial cells quadrate, thin-walled, stomates present, annulus of 2 rows, quadrate, thick-walled, operculum mammillate to rostellate, peristome present, fully developed, perforated in distal half.

Exposed, acidic granite and sandstone, high elevation forests to tundra; 880--3700 m; Greenland; Alta., B.C., Labr., N.W.T., Que., Yukon; Alaska, Col., Idaho, Maine, Mont., N.H., N.Y., Oreg., Utah, Wash., Wyo.; Mexico; South America; Eurasia; Africa; Antarctic.

Grimmia donniana is widespread but relatively uncommon and sporadic along the front ranges of the Rocky Mountains from Alberta down to southern Utah and Colorado. In the west it is also known from a few locations in central Washington, northern Idaho, and northern Oregon. It is rare at higher latitudes with a few records from Alaska, the Yukon, Northwest Territories, and Greenland. There are two disjunct populations in eastern North America, one in the New England states and southern Quebec, and the other in Labrador. Most specimens reported from British Columbia (R. R. Ireland et. al, 1987) are in error, most being Grimmia alpestris. Grimmia donniana is usually recognized by (1) leaves with plane margins and (2) a hyaline rather uniform basal lamina with long-rectangular, thin-walled cells. The leaves of Grimmia montana, while often incurved distally, may also have plane margins. The latter species, however, has quadrate to short-rectangular basal marginal cells with thick end-walls and is rarely hyaline. It is also dioicous and lacks stomates. Grimmia sessitana can also have leaves with plane margins, but often one margin is recurved. Its basal marginal laminal cells are also rectangular, but have thick rather than thin walls and is not hyaline. The leaf cells of G. sessitana are most often bulging, mammillose; those of G. donniana are not. H. C. Greven has observed that specimens of Grimmia incurva have often been misidentified as G. donniana (see discussion of G. incurva).