1. Rhytidium rugosum (Hedwig) Kindberg, Bih. Kongl. Svenska Vetensk.-Akad. Handl. 7(9): 15. 1883.
Hypnum rugosum Hedwig, Sp. Musc. Frond., 293. 1801
Plants to 10 cm, yellowish green to golden brown. Stems 2-3 mm wide across leafy stem, turgid from crowded leaves, often hooked at apices, branches to 10 mm. Stem leaves 2.8-4.5 × 0.8-1.5 mm; alar cells many, 8-20 × 8-12 µm, region broad, triangular, along margin; medial laminal cells 25-55 × 4-6 µm. Branch leaves 1.2-2.3 × 0.4-0.8 mm. Seta 2-2.5 cm. Capsule 2-2.5 mm.
Capsules mature summer. Rock, thin layer of soil or humus overlying rock, calcareous or mafic, exposed rock ledges, rocky slopes, bluffs, semi-open dry forests, in tundra, much less common on moist sites; low to high elevations (100-3900 m); Greenland; Alta., B.C., Man., N.B., Nfld. and Labr., N.W.T., N.S., Nunavut, Ont., Que., Sask., Yukon; Alaska, Ariz., Colo., Conn., Ill., Ind., Iowa, Ky., Maine, Md., Mass., Mich., Minn., Mo., Mont., N.H., N.J., N.Mex., N.Y., N.C., Ohio, Oreg., Pa., S.Dak., Tenn., Tex., Vt., Va., W.Va., Wis., Wyo.; Mexico; Central America (Guatemala); South America (Bolivia); Eurasia; Africa (Kenya, Morocco, Uganda).
Though widespread, Rhytidium rugosum is infrequent, presumably because of a preference for exposed calcareous or mafic bedrock in a cool habitat. The plants are rarely found with sporophytes; perhaps almost total reliance on asexual reproduction explains the strong morphological uniformity seen among specimens of R. rugosum collected from across its broad range.