Bull. Torrey Bot. Club 25: 128. 1898.
Plants on rock or terrestrial, forming loose mats. Stems radially symmetric, long to short-creeping, not readily fragmenting, ± regularly forked, without budlike arrested branches, tips straight; main-stem indeterminate, lateral branches determinate, 1–2-forked. Rhizophores borne on upperside of stems, throughout stem length, 0.13–0.23 mm diam. Leaves monomorphic, in ± alternate pseudowhorls of 3, tightly appressed, ascending, green, lanceolate to linear-lanceolate or lanceolate-elliptic, 1–2 × 0.45–0.6 mm; abaxial ridges well defined; base rounded and adnate, sometimes slightly decurrent, pubescent or glabrous; margins ciliate to denticulate, cilia transparent, spreading or ascending, 0.03–0.17 mm; apex keeled, obtuse or slightly attenuate, nearly truncate in profile, blunt to short-bristled; bristle transparent to greenish transparent or whitish, smooth, 0.06–0.45 mm. Strobili solitary, (0.6–) 1–3 cm; sporophylls ovatelanceolate, ovate-elliptic, or deltate-ovate, abaxial ridges well defined, base glabrous, margins ciliate to denticulate, apex strongly to slightly keeled, short-bristled to blunt. 2n = 18.
Ariz., Colo., N.Mex., Tex., Utah, Wyo., only in the flora
Selaginella mutica, S. underwoodii (R. M. Tryon 1955; C. A. Weatherby 1943), and S. wallacei all have similar patterns of variation. Study is needed to assess to what degree such variability is caused by environmental or genetic factors. Within S. mutica, two rather distinct, morphologic extremes are recognized here as varieties. Many specimens having leaves with spreading, long, marginal cilia and a short, broken, apical bristle have been considered intermediate between the two varieties, but they belong in S. mutica var. mutica.
Selaginella mutica may be one of the parent species of the putative hybrid species S. × neomexicana (see discussion). Selaginella mutica is often found growing in the same habitat with S. underwoodii, S. × neomexicana, and S. weatherbiana. According to R. M. Tryon (1955), where the two grow together, S. mutica mats gradually entirely replace mats of S. underwoodii over time. Selaginella mutica is sometimes confused with S. viridissima.
|1||Margins of sporophylls usually long-ciliate, seldom denticulate, cilia spreading; apex of leaves with or without bristle, 0.03–0.06 mm; leaf margins long- ciliate, rarely denticulate, cilia spreading.||Selaginella mutica var. mutica|
|1||Margins of sporophylls mostly very short-ciliate to denticulate, cilia and teeth ascending; apex of leaves with bristle 0.2–0.45 mm; leaf margins short-ciliate to denticulate, cilia and teeth ascending.||Selaginella mutica var. limitanea|