Proc. Acad. Nat. Sci. Philadelphia 99: 185. 1947.
Herbs or subshrubs, perennial, 3–4 dm; from a woody caudex; with woody roots. Stems few to several, ± prostrate, sometimes ascending, much-branched, with dense, matlike growth-form, often with short, leafy axillary shoots, hairs dense, tangled, short to long, fairly stiff, branched, sometimes glandular, white-woolly. Leaves green to deep purple, narrowly elliptic to oblong, ovate, or obovate, 1–3 cm, ± fleshy, margins plane or ± wavy, flat, 0-lobed, apex rounded, rarely acute. Inflorescences usually erect, 2.5–8 × 1.5–4 cm; bracts proximally greenish, distally pale to bright-yellow, sometimes brownish orange, sometimes with brownish orange medial band, oblong, elliptic, or obovate, ± cupshaped, ± fleshy, 0–3-lobed; lobes erect, oblong, short, arising near tip, central lobe apex rounded to truncate, sometimes crenate or with obtuse teeth, lateral ones obtuse. Calyces colored as bracts, lacking orange central band, 16–23 mm; abaxial clefts 9.5–14 mm, adaxial 8 mm, abaxial 50–67% of calyx length, adaxial 35–45% of calyx length, deeper than laterals, lateral 4.5–5 mm, 20–25% of calyx length; lobes oblong to triangular, abaxials sometimes wider than adaxials, apex acute to rounded, inner surface glabrous. Corollas straight, 17–26 mm; tube 12–13 mm; beak often slightly exserted, adaxially green to yellow-green, 11–13 mm; abaxial lip green, reduced, 1.5–3.5 mm, 10–20% as long as beak; teeth incurved, reduced, green, 0.5–1 mm. 2n = 24.
Phenology: Flowering Apr–Aug.
Habitat: Sandy openings in coastal scrub, thin sandy soils over limestone terraces, north- or northwest-facing sandy bluffs, dunes.
Elevation: 0–100 m.
Castilleja mollis is federally listed as a threatened species under the Endangered Species Act of the United States. It is endemic to the coastal terraces of the northern portion of Santa Rosa Island, Santa Barbara County, in the northern Channel Islands of southern California. It is recorded historically from San Miguel Island. Much of the available low-elevation habitat on Santa Rosa Island was degraded by trampling and grazing of introduced ungulates, which also resulted in the apparent loss of a natural population on the western end of San Miguel Island, last seen in the 1930s and now believed extirpated. Reports of C. mollis from the Oso Flaco Lake area of the mainland, in San Luis Obispo County, are based on populations of C. affinis var. contentiosa. Castilleja mollis is most closely related to C. latifolia of the central California coast and a sister species to the north, C. mendocinensis.