Bull. Torrey Bot. Club 31: 644. 1905.
Herbs, perennial, 0.8–1.5 dm; from a woody caudex; with a taproot. Stems few to several, erect or ascending, unbranched, sometimes branched, hairs retrorse, short, soft, eglandular. Leaves green to purple, linear to linear-lanceolate, 2–3.3 cm, not fleshy, margins plane, involute, 0–3(–5)-lobed, apex acuminate; lobes ascending-spreading to widely spreading, narrowly linear, apex acute. Inflorescences 4–5 × 1.5–2.5 cm; bracts greenish throughout, or proximally greenish, distally bright yellow, yellow-green, or yellow-orange on apices, narrowly lanceolate to linear-lanceolate, 0–5(–7)-lobed; lobes spreading, filiform to linear, long, proximal lobes arising in proximal 1/2, apex acute to acuminate. Calyces light green to yellowish, margins sometimes yellow, 10–17 mm; abaxial clefts 8–9 mm, adaxial 2–3 mm, abaxial ca. 50% of calyx length, adaxial ca. 20% of calyx length, deeper than laterals, lateral 1.9–2.5 mm, 12–20% of calyx length; lobes narrowly triangular, apex acute to acuminate. Corollas straight or slightly curved, 18–21 mm; tube 13–15 mm; beak exserted, adaxially yellow to yellow-green, 6–8 mm; abaxial lip green, reduced, visible in front cleft, slightly pouched, 2.5–3.5 mm, 35–60% as long as beak; teeth erect, yellow, 1 mm. 2n = 24.
Phenology: Flowering (Feb–)Jul–Aug.
Habitat: Moist meadows, stream banks, mesic rocky slopes, tundra, subalpine and alpine.
Elevation: 2700–3900 m.
Castilleja puberula is a near-endemic of alpine communities in the Rocky Mountains of Colorado in Boulder, Clear Creek, Gilpin, Grand, Larimer, and Park counties. A highly disjunct population occurs near the summit of Mt. Jefferson on the Continental Divide in Beaverhead County, Montana. Castilleja puberula appears to be a high-elevation isolate from the widespread C. flava, which is common at lower elevations in the Intermountain Region. A single case of hybridization with C. septentrionalis is known from Clear Creek County.