Plants on rock, forming loose festoonlike mats or rarely compact mats. Stems radially symmetric, long-creeping, short-creeping, or pendent, not readily fragmenting, irregularly forked, without budlike arrested branches, tips straight; main stem indeterminate, lateral branches determinate, spreading, 1--2-forked. Rhizophores borne on upperside of stems, throughout stem length, 0.15--0.27(--0.3) mm diam. Leaves monomorphic, in alternate pseudowhorls of 4 (on main stem and older lateral branches) or 3 (on young lateral branches and secondary branches), loosely appressed, ascending, green, linear to linear-lanceolate or narrowly triangular-lanceolate, (2--)2.5--3.4 X 0.45--0.5(--0.7) mm; abaxial ridges prominent; base mostly cuneate and decurrent, rarely rounded and adnate (on young branches), pubescent or glabrous; margins entire to denticulate or very short-ciliate, cilia transparent, scattered, mostly ascending, dentiform toward apex, 0.02--0.07 mm; apex keeled, slightly attenuate, short- to long-bristled; bristle transparent greenish to greenish-yellowish, rarely white, smooth, seldom slightly puberulent, sometimes breaking off, 0.25--0.7(--1) mm. Strobili sometimes paired, 0.5--3.5 cm; sporophylls lanceolate to ovate-lanceolate, abaxial ridges prominent, base glabrous, with prominent auricles (no other species has such prominent auricles), margins entire or very short-ciliate to denticulate, apex keeled, short- to long-bristled. Moist or shaded cliffs, rocky slopes, rock crevices, granitic outcrops, hanging over granite cliffs, sandstone or limestone ledges; (800--)1500--3000(--4000) m; Ariz., Colo., N.Mex., Okla., Tex., Utah, Wyo.; Mexico in Chihuahua and Nuevo León. R. M. Tryon (1971) reported that the bristle on Selaginella underwoodii leaves is longer (to 1.44 mm) in the southern part of the range and shorter (to 0.43 mm) northward and in central Arizona. Selaginella underwoodii seems to be closely related to S . oregana , perhaps sharing a common ancestor.

STEMS: monomorphic, prostrate to loosely ascending, occasionally pendant, not readily fragmenting when dry, the branch tips appearing straight when dry, forming usually loose mats. RHIZOPHORES: produced throughout. LEAVES: monomorphic, 2.0–3.5 mm long, linear to narrowly triangular-lanceolate, green to dark green when hydrated, the base more or less decurrent (similar in color to the stem) and more or less symmetrically narrowed, the tip with a straight or somewhat curved yellowish green seta 0.2–0.8(–1.2) mm long 44 CANOTIA Vol. 5 (1) 2009(sometimes breaking off with age), the margins short-ciliate, sometimes grading to denticulate distally. STROBILI: 5–30 mm long, the sporophylls lanceolate to broadly lanceolate with a strongly auriculate base, narrowed to an acute tip with a short seta, the margins denticulate, sometimes grading to short-ciliate proximally. MEGASPORES: finely rugose-reticulate, orange. NOTES: Rock outcrops, ledges, boulders, and cliffs, on various substrates: Cochise, Coconino, Gila, Graham, Pima, Santa Cruz, Yavapai cos. (Fig. 1G); 1500–2450 m (5000–8000 ft); UT and s CO s to AZ and TX; n Mex. REFERENCES: Yatskievych, G. and M. D. Windham. Vascular Plants of Arizona: Selaginellaceae. CANOTIA 5 (1): 39–48, 2009.

General: Loose mats to compact mats on rock, with radially symmetrical stems, long–creeping to pendent, irregularly forked, with straight tips, indeterminate main stem and determinate lateral stems that spread, 1–2 forked, freely branching and rooting throughout; rhizophores borne on upperside of stems, throughout stem length, 0.15–0.27 mm in diameter. Leaves: Monomorphic, brilliant dark green when young, in alternate pseudowhorls of 4 on both main and lateral branches, loosely appressed, ascending, linear to linear-lanceolate or narrowly triangular-lanceolate, 2.5-3.4 mm by 0.45-0.5 mm with prominent ridges below; base cuneate and decurrent, rarely rounded and adnate, pubescent to glabrous; margins entire to denticulate or very short ciliate, cilia transparent, scattered, mostly ascending; apex keeled, slightly attenuate, short to long bristled, bristle transparent greenish to greenish yellow, rarely white, 0.25-0.7 mm. Sporangia: Strobili sometimes paired, 0.5-3.5 cm, sporophylls lanceolate to ovate-lanceolate, lower ridges prominent, base glabrous with prominent auricles, entire to short ciliate margins. Ecology: Found on moist or shaded cliffs, on rocky slopes, in crevices, or granitic outcrops, or even sandstone or limestone ledges from 5,000-8,000 ft (1524-2438 m). Notes: The prominent auricles on the strobili is distinctive to this species. Also identifiable by its brilliant green leaves and its preference for more mesic habitats. Etymology: Selaginella is a diminutive of Selago, the name of another similar plant, while underwoodii is named for Lucien Marcus Underwood (1853-1907) an American botanist who studied ferns. Sources: FNA 1993, Dittmer et al. 1954, Kearney and Peebles 1969