Bull. S. Calif. Acad. Sci. 42: 31. 1943.
Subshrubs or shrubs, perennial, 4–6(–10) dm, to 20 dm wide; from a woody caudex; with thick, woody roots. Stems many, spreading and ascending, much-branched, with short, leafy axillary shoots, proximal stems 1+ cm wide, hairs dense, spreading, matted, white, medium length, soft, stellate, sometimes mixed with short stipitate-glandular ones especially near inflorescence, partially obscuring surface. Leaves ash gray, linear to narrowly lanceolate, 1–6.5 cm, not fleshy, margins plane or slightly wavy, involute, 0–7-lobed, apex rounded to obtuse, surfaces almost obscured by hairs, at least when young; lobes spreading to ascending, linear to narrowly oblong, apex acute to acuminate. Inflorescences (3–)7.5–11.5 × 1.5–3.5 cm; bracts proximally greenish, distally ± pale yellow, proximals sometimes greenish throughout, linear to narrowly lanceolate or narrowly oblong, (3–)5–7-lobed; lobes spreading, linear to narrowly oblong, long, proximal lobes arising below mid length, apex obtuse to acute. Calyces colored as bracts, 10–20 mm; abaxial and adaxial clefts 5.5–7 mm, 50% of calyx length, deeper than laterals, lateral 0–1 mm, 0–8% of calyx length; lobes oblong, apex truncate to rounded or obtuse, rarely emarginate, inner surface glandular. Corollas curved in proximal 1/3, 15–25 mm; tube 11 mm; abaxial lip not exserted, sometimes visible in abaxial cleft, beak exserted; beak adaxially green or dull yellow, 7–9 mm; abaxial lip deep green, reduced, 1–2 mm, less than 25% as long as beak; teeth incurved, green, 0.7–1 mm. 2n = 24.
Phenology: Flowering Feb–Jun.
Habitat: Coastal terraces and slopes, cliffs and canyon walls, coastal sage scrub.
Elevation: 0–500 m.
Castilleja grisea is endemic to a small portion of San Clemente Island in Los Angeles County, which is managed by the U.S. Navy. It was one of the first plants listed as endangered under the Endangered Species Act of the United States, and its near extinction was due to grazing by feral goats. Plants responded well when the goats were removed, spreading from their last refuge on inaccessible cliffs onto gentle terrain at the southern end of the island, near the type locality, and are now locally fairly common. Ungrazed old shrubs can reach 1 m in height and 2 m in breadth and often have a thick woody trunk. The stellate pubescence is unusual in Castilleja.
Castilleja grisea is in the Center for Plant Conservation’s National Collection of Endangered Plants.