Bull. Torrey Bot. Club 34: 40. 1907.
Herbs, perennial, 1–2 dm; from a woody caudex; with a taproot or stout, branched roots. Stems several to many, decumbent to ascending, unbranched except for small, leafy axillary shoots, hairs retrorse, short proximally, spreading, longer distally, soft, stipitate-glandular. Leaves green to blackish, proximalmost small and scalelike, linear to narrowly or broadly lanceolate, 1–3 (–4) cm, not fleshy, margins plane, involute, 0 (–3) -lobed, apex obtuse to rounded; lobes ascending, linear or short-lanceolate, very small, apex acute to obtuse. Inflorescences 4–6.5 × 1–3 cm; bracts proximally greenish to deep purple near base, distally magenta, deep pink, or red, broadly lanceolate to elliptic, oblong, or ovate, 0–5-lobed; lobes ascending to erect, triangular to oblong, short, arising near apex, central lobe apex rounded, lateral ones acute to rounded. Calyces colored as bracts, 12–18 mm; abaxial and adaxial clefts 5.5–8.5 (–10) mm, ca. 50% of calyx length, deeper than laterals, lateral 1–3 (–5) mm, ca. 25% of calyx length; lobes broadly linear or narrowly triangular, apex acute to obtuse, sometimes rounded. Corollas straight, 16–24 mm; tube 10–13 (–15) mm; beak exserted, adaxially green, 4.5–8 (–9) mm; abaxial lip green to deep purple, reduced, 1–3 mm, 40–45% as long as beak; teeth incurved, greenish, (0.5–) 1–2.5 mm. 2n = 24.
Phenology: Flowering Jun–Aug.
Habitat: Gravelly meadows, rocky slopes, talus, ridges, krummholz zone or alpine.
Elevation: 2700–3700 m.
Castilleja parvula is limited to the upper elevations of the Tushar Mountains. Morphologically, it appears to be a species derived from the widespread Rocky Mountains species C. rhexiifolia.