Plants on rock or terrestrial, forming clumps. Stems radially symmetric, underground (rhizomatous) and aerial, not readily fragmenting, irregularly forked; rhizomatous and aerial stems often with 1 branch arrested, budlike, tips straight; aerial stems erect or occasionally ascending. Rhizophores borne on upperside of stems, restricted to rhizomes and lower 1/3 of aerial stems, 0.3--0.4 mm diam. Leaves dimorphic, not clearly ranked. Rhizomatous stem leaves persistent, tightly appressed, scalelike. Aerial stem leaves appressed, ascending, green, linear-lanceolate to narrowly lanceolate, 2.2--3.8 X 0.29--0.4(--0.75) mm; abaxial ridges present; base abruptly adnate, cordate to almost peltate, pubescent or sometimes glabrous; margins short-ciliate at base, denticulate toward apex, cilia white to transparent or greenish, spreading at base, ascending toward apex, 0.02--0.08 mm; apex keeled, bristled; bristle puberulent, rough, transparent to whitish, 0.23--0.75 mm. Strobili solitary, (0.4--)1--1.5 cm; sporophylls ovate-lanceolate to lanceolate, abaxial ridges not prominent, base glabrous, margins short-ciliate to denticulate, apex bristled. 2 n = 18.

Exposed rock crevices, cliffs, boulders, sandstone or igneous rock, serpentine, or gravelly soil; 0--2000 m; Calif.; Mexico in Baja California.

Selaginella bigelovii is a member of the series Arenicolae (R. M. Tryon 1955) and is closely related to S . rupincola (see discussion). It may be confused with S . × neomexicana . Selaginella bigelovii , however, always has well-developed megasporangia with most of the megaspores and microspores well formed, whereas S . × neomexicana is a presumed sterile hybrid that does not form megaspores, seldom forms microspores, and usually has most sporangia misshapen (R. M. Tryon 1955). Moreover, S . × neomexicana has not been reported from either California or Baja California.