Syst. Bot. 16: 657. 1991.
Herbs, annual, 1.5–4.5 dm; with fibrous-roots. Stems solitary or few, erect, unbranched or branched, hairs spreading, short to long, ± stiff, mixed with short-stipitate-glandular ones. Leaves green, linear to narrowly lanceolate or narrowly oblong, 2–5.7 cm, not fleshy, margins plane, flat, 3–7 (–9) -lobed, apex acuminate to acute; lobes spreading to ascending, linear to narrowly oblong, apex acuminate. Inflorescences 2–14 × 1–4 cm; bracts greenish throughout, or proximally greenish, distally white, cream, pale-pink, or pale-purple on apices, linear-lanceolate, 5–7 (–9) -lobed, sometimes with secondary lobes; lobes ascending to spreading, linear to narrowly oblanceolate, long, arising all along leaf axis, apex acute to obtuse. Calyces colored as bracts, 15–25 mm; all 4 clefts subequal, 7–11 mm, 50–67% of calyx length; lobes linear, apices often slightly expanded, apex obtuse to acute. Corollas straight or slightly curved, 12–25 mm; tube 9–14 mm, expanded distally; abaxial lip sometimes slightly exserted, never hidden by slender calyx lobes, beak exserted; beak straight, adaxially white or lilac pink, 3–5.5 mm, inconspicuously puberulent; abaxial lip proximally white, distally yellow, with purple or redbrown spots, conspicuous, pouches 3, inflated, 4–6 mm, 4–5 mm wide, 2 mm deep, longer than deep, 1.5–4 mm, 90% as long as beak; teeth erect, white, usually with purple spot at base, 0.5–1 mm. Filaments glabrous. 2n = 20.
Phenology: Flowering Apr–Jun(–Jul).
Habitat: Grasslands, moist meadows, swales, shores, forest openings.
Elevation: 0–1600 m.
Castilleja lineariloba is endemic to the western slope of the Sierra Nevada. Its chromosome number is 2n = 20, an apparent aneuploid reduction and documented by numerous counts. This diploid number is shared only with two very distantly related annual species endemic to central Mexico, C. gracilis Bentham and C. tenuifolia M. Martens & Galeotti.