Hypnum rugosum Hedwig
Plants 2--3 mm wide measured across leafy stem, to 10 cm long, yellowish-green to golden brown; stems and branches turgid because of crowded leaves; stems often hooked at tips; branches mostly short, up to 10 mm. Stem leaves 2.8--4.5 × 0.8--1.5 mm; costa sometimes forked; median cells 25--55 × 4--6 µ m; alar cells numerous, in a broad triangular area extending up leaf margin, 8--20 × 8--12 µ m. Branch leaves 1.2--2.3 × 0.4--0.8 mm. Seta 20--25 mm. Capsule 2--2.5 mm.
Mostly on rock or on thin layer of soil or humus overlying rock, especially of calcareous or mafic composition; commonly on exposed rock ledges, rocky slopes, or bluffs, or in semi-open dry forests or in tundra, much less common on moist sites; 100--3900 m; Greenland; Alta., B.C., Man., Nfld., N.W.T., N.S., Nunavut, Ont., Que., Sask., Yukon; Alaska, Ariz., Colo., Conn., Ind., Iowa, Ky., Maine, 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.
Even though it is widespread, Rhytidium rugosum is infrequent, presumably because of a preference for exposed calcareous or mafic bedrock in a cool habitat. The species is 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.