Plants in small cushions, dark green to brown. Stems 0.5--1 cm. Stem leaves oblong-ovate to oblong-lanceolate, 0.9--2 × 0.4--0.8 mm, concave, awn 0.1--1.2 mm; distal laminal cells 1-stratose with 2-stratose patches, marginal cells 2-stratose; medial laminal cells quadrate, sinuose, thick-walled; basal juxtacostal laminal cells quadrate to long-rectangular, straight, thin-walled; basal marginal laminal cells quadrate to long-rectangular, straight, thin-walled. Sexual condition gonioautoicous. Seta sigmoid, 0.2--0.3 mm. Capsule usually present, exothecial cells thin-walled, annulus of 1--2 rows, quadrate, thin-walled, operculum mammillate, peristome absent.

Exposed, calcareous sandstone, limestone, and concrete; 25--2700 m; Greenland; Alta, B.C., N.B., N.W.T., Nunavut, Ont., Que., Sask., Yukon; Alaska, Ariz., Calif., Colo., Idaho, Mich., Mont., Nev., N.Mex., N. Dak., Oreg., S.Dak. Utah, Wash., Wyo.; ne Mexico; South America (Bolivia, Chile); Eurasia; Africa (Morocco).

Grimmia anodon is widespread and common across the western United States and the mountains of southern Alberta and British Columbia. It is absent from eastern North America except around the Great Lakes and individual sites in the Gaspe Peninsula and New Brunswick. It extends sparsely into the Yukon and Alaska. These high latitude sites are strongly correlated with glacial refugia or areas of early deglaciation. Most eastern United States collecting localities are near the margin of the Wisconsinan continental ice sheet. The west-east disjunction of the species suggests the disruption of a more continuous distribution by Wisconsinan glacial events. However, limited bedrock outcrops in the midwest limits habitat availability in that region. Grimmia anodon is widespread in the northern hemisphere on calcareous outcrops and disturbed sites. Usually fertile, G. anodon is recognized easily by its immersed, gymnostomous capsule, on a sigmoid seta. The other widespread species in the subgenus, Grimmia plagiopodia, has peristome teeth. If sterile these species can be difficult, but G. anodon has concave leaves with 2-stratose margins, while G. plagiopodia has leaves tending to be more keeled and they are uniformly 1-stratose. Grimmia anodon is rather similar to Schistidium flaccidum (De Not.) Ochyra. However, this latter species is characterized by a short, straight seta, leaves sharply keeled distally, leaf margins plane at base but recurved distally on both sides.