Plants terrestrial or on rock, forming cushionlike or rather loose mats. Stems decumbent or creeping, not readily fragmenting, irregularly forked, without budlike arrested branches, tips straight; main stem upperside and underside structurally slightly different, conspicuously or inconspicuously indeterminate, lateral branches radially symmetric, conspicuously determinate, strongly ascending, 1--2-forked. Rhizophores borne on upperside of stems, throughout stem length, 0.25--0.45 mm diam. Leaves monomorphic, in poorly defined pseudowhorls of 4 or 6, tightly appressed, ascending, green, linear-lanceolate to linear, in lateral ranks sometimes falcate, 2.5--4(--4.3) X 0.5--0.75 mm (upperside leaves smaller than underside, smaller also on ascending buds); abaxial ridges present; base (on main stem) decurrent, oblique, and glabrous on underside leaves, slightly decurrent to adnate, oblique, and glabrous or rarely puberulent on upperside leaves; margins usually short-ciliate, cilia transparent, spreading or ascending at base, denticulate and ascending on distal 2/3, 0.02--0.07(--0.15) mm; apex plane or sometimes slightly keeled, obtuse to attenuate, abruptly bristled; bristle whitish, transparent to opaque, with few teeth or smooth, 0.5--1.1 mm. Strobili solitary, (0.5--)1--3(--4.5) cm; sporophylls ovate-lanceolate, lanceolate, or seldom ovate, usually tapering toward apex, abaxial ridges well defined, base glabrous, margins proximally short-ciliate to denticulate, lacking cilia apically, apex usually attenuate or slightly keeled, short-bristled. Rocky alpine tundra, subalpine meadows, dry cliffs, rocky slopes, rock crevices, granitic outcrops and ledges, sandstone outcrops, in soil pockets among rocks, or sandy or granitic soil; 700--3700 m; Alta., B.C.; Ariz., Calif., Colo., Idaho, Mont., N.Mex., Oreg., Utah, Wash., Wyo. Selaginella scopulorum is a member of the S . densa complex, in which there is a clear need for more systematic studies. Some specimens of S . scopulorum from Montana, Wyoming, and Colorado have more conspicuous whitish bristles than those elsewhere and are difficult to distinguish from S . densa .