Ann. Lyceum Nat. Hist. New York 2: 230. 1827.
Herbs, perennial, 0.7–2(–3) dm; from a small, woody caudex; with a taproot. Stems several to many, erect or ascending, usually short-decumbent at base, unbranched, sometimes glabrous proximally, hairs spreading, long, soft, mixed with medium length to short stipitate-glandular ones only in inflorescence. Leaves green to deep purple, linear-lanceolate to broadly lanceolate (to linear on sterile shoots), 1.5–4(–5.5) cm, not fleshy, margins plane, flat, prominently veined, 0–3(–5)-lobed, apex acute to rounded; lobes ascending, lanceolate, apex acute. Inflorescences 2–7(–10) × 1–3.5 cm; bracts greenish to pale greenish yellow throughout, often aging dull reddish brown or reddish purple proximally, rarely dull reddish brown throughout, or proximally green, dull reddish brown, or reddish purple, distally greenish white, yellow, or cream, broadly lanceolate to widely oblong to ovate, 0–3(–7)-lobed; lobes ascending, triangular to lanceolate, medium length, usually arising at or above mid length, rarely just below, central lobe apex obtuse to rounded, others acute. Calyces proximally green to purple, distally colored as bracts, 12–20 mm; abaxial and adaxial clefts 5–9(–10) mm, 40–50% of calyx length, deeper than laterals, lateral 1–3(–4.5) mm, 5–20% of calyx length; lobes lanceolate to triangular, apex acute, obtuse, or rounded. Corollas straight, 16–25 mm; tube 9–15 mm; teeth and part of abaxial lip sometimes exserted, beak exserted; beak adaxially green, (2.5–)5–9 mm; abaxial lip green, reduced, often visible through abaxial cleft, slightly pouched, 1.5–3 mm, 25–50% as long as beak; teeth incurved to ascending, white, sometimes green, 0.7–2 mm. 2n = 24, 48.
Phenology: Flowering Jun–Sep.
Habitat: Meadows, gravel slopes, talus, ridges, mostly upper subalpine to alpine.
Elevation: 1500–4300 m.
Alta., B.C., Colo., Mont., N.Mex., Utah.
Castilleja occidentalis has a wide distribution in the southern Rocky Mountains, a gap in its distribution in Wyoming, and reappears in Montana and the Canadian Rockies. Bract lobing and color vary considerably but without correlation to geography. Although C. occidentalis resembles an alpine form of C. septentrionalis, C. occidentalis is missing in several regions in the distribution of the latter, even when extensive areas of suitable habitat are available, and has a discrete range.