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 X 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 ovate-lanceolate, ovate-elliptic, or deltate-ovate, abaxial ridges well defined, base glabrous, margins ciliate to denticulate, apex strongly to slightly keeled, short-bristled to blunt. 2 n = 18. 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 .

STEMS: monomorphic, the main stem prostrate, with prostrate to loosely ascending branches, not readily fragmenting when dry, the branch tips appearing straight when dry, forming loose mats. RHIZOPHORES: produced throughout. LEAVES: monomorphic, 1–2 mm long, narrowly lanceolate to narrowly elliptic-lanceolate, green to dark green when hydrated, the base adnate (differing in color from the stem) and more or less symmetrically rounded or narrowed, the tip bluntly or sharply pointed, with or without a seta, the margins short- to long-ciliate, sometimes mostly denticulate. STROBILI: 6–25 mm long, the sporophylls narrowly ovate to elliptic-ovate or ovate-deltate, narrowed to a blunt or sharply pointed tip with or without a short seta, the margins denticulate to ciliate. MEGASPORES: finely to relatively coarsely rugose-reticulate, orange. NOTES: 2 vars.; WY s to AZ and TX. NOTES: 2 vars.; WY s to AZ and TX. REFERENCES: Yatskievych, G. and M. D. Windham. 2009. Vascular Plants of Arizona: Selaginellaceae. CANOTIA 5 (1): 39–48.

General: Forming loose mats, plants on rock or earth, with stems radially symmetric, long to short creeping, 1-2 forked. Leaves: Monomorphic, in pseudowhorls of 3, these tightly appressed and ascending, green and linear-lanceolate to lanceolate-elliptic, each 1-2 mm long and less than a half mm wide. Ridges below well defined, the base rounded and adnate, the margins with ciliate hairs to small dentations these minute, the apex is keeled and attenuate, blunt to short bristled. Sporangia: Solitary strobili, 1-3 cm, with ovate lanceolate sporophylls, ovate-elliptic, with a glabrous base and ciliate to denticulate margins. Notes: “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.”  (FNA 2003). The two varieties: var. mutica and var. limitanea. Etymology: Selaginella is a diminutive of Selago, the name of another similar plant, while mutica means blunt without a point. Sources: FNA 1993