STEMS: dimorphic, not readily fragmenting when dry, the branch tips appearing straight when dry, forming loose low clumps, differentiated into a rhizomatous, prostrate, main stem system with elongated procumbent or more commonly ascending to erect main branches, some of the basal branches of the aerial stems (and rhizomes) remaining bud-like and not elongating. RHIZOPHORES: of the aerial stems produced only below the midpoint. LEAVES: dimorphic, those of the rhizomes 1.5–2.5 mm long, ovate to narrowly ovate, persistently gray to tan, the midvein slightly ridged, the base more or less adnate (not strongly different in color to the stem), the tip sharply pointed, without a seta, the margins denticulate to nearly entire; aerial stem leaves 3.0–4.7 mm long, narrowly elliptic-lanceolate to linear-lanceolate, light grayish green, the minutely puberulent base adnate (different in color from the stem) and rounded, the tip sharply pointed, with a white to pale yellow seta 0.7–1.8 mm long, this often bent outward, denticulate, the margins relatively long-ciliate, the cilia spreading. STROBILI: 5–30 mm long, the sporophylls lanceolate, tapered to an acute tip, with a well-developed seta, the margins short-ciliate. MEGASPORES: finely rugose to rugose-reticulate, orange. NOTES: Rock ledges, cliffs, and open gravelly to rocky areas, usually on igneous or volcanic substrates or on sandstone: Cochise, Gila, Pima, Pinal, Santa Cruz cos. (Fig. 1F); 900–1850 m (3000–6000 ft); s AZ to s TX; Mex. For a discussion of possible hybridization with S. arizonica, see the treatment of that species. Tryon (1955) discussed the sporadic distribution in southern Arizona, New Mexico, and Texas of the rare S. ×neomexicana Maxon, which he thought to represent a sterile hybrid between S. rupincola and S. mutica, citing a single historical Arizona collection (Ferris s.n., March 1904, GH, US) from near Paradise (Cochise County). Aside from its abortive spores, this taxon closely resembles S. rupincola, but has leaves with shorter setae and the margins denticulate distally and with short ascending ciliation proximally. Valdespino (1993) suggested that more detailed biosystematic research is necessary to confirm the parentage of this putative hybrid. The report of S. ×neomexicana from Graham County by Buegge (2001) was based upon a misdetermined specimen of S. rupincola. REFERENCES: Yatskievych, G. and M. D. Windham. Vascular Plants of Arizona: Selaginellaceae. CANOTIA 5 (1): 39–48, 2009.