Plants terrestrial or on rock, forming rosettes. Main (central) stem spirally compact, branched, branches 2--3-forked, prostrate, flat when moist, almost flat when dry, not articulate, glabrous. Rhizophores borne on underside of stems, restricted to base of rosette, 4--5 mm diam. Leaves thick and stiff. Lateral leaves overlapping, ascending, green, elliptic to elliptic-ovate, (2--)3--3.5 X 0.8--1 mm; base cordate, with 2 ciliate lobes or auricles; margins transparent, acroscopic margins short-ciliate at base, dentate toward apex; basiscopic margins entire to scattered dentate; apex bristle 1/3--1/2 length of leaf blade. Median leaves peltate, oblique-lanceolate, 2--3 X 0.7--1 mm; base rounded to truncate, pubescent; margins green to slightly transparent, inner margins dentate, outer margins entire or slightly dentate; apex bristle 1/3 length of leaf blade. Strobili solitary, 5--10 mm; sporophylls monomorphic, lanceolate-ovate, slightly keeled, keel not dentate, base pubescent, margins transparent to greenish, short-ciliate to denticulate, apex long-bristled. 2 n = 20. Dry rocky soil, rock crevices, limestone rock, and cliff faces; of conservation concern; 1500--2500 m; N. Mex., Tex.; n Mexico. Selaginella lepidophylla Mettenius is a misapplied name. The long-bristled leaf apex of Selaginella pilifera is unique among New World xerophytic members of subg. Stachygynandrum series Circinatae Spring. The closest relative of S . pilifera is S . gypsophila A. R. Smith & T. Reeves, which is from Nuevo León, Mexico, and differs by having obtuse leaf apices. Further studies are needed to determine whether S . gypsophila represents a well-differentiated species or an environmental variant of S . pilifera .