Bot. Gaz. 42: 146. 1906.
Herbs, perennial, (1.5–)2–4 dm; from a woody caudex; with branched, woody roots. Stems few or several, ascending to erect, branched or unbranched, shiny proximally, glabrous proximally, hairy distally, hairs spreading, long, soft, eglandular, sometimes sparsely glandular. Leaves deep purple to green, linear-lanceolate to narrowly lanceolate, rarely broadly lanceolate, 1.5–4.5 cm, not fleshy, margins plane, flat or slightly involute, 0(–3)-lobed, apex usually acuminate or acute; lobes upright or ascending, lanceolate, apex acute. Inflorescences 2–12 × 2–6 cm; bracts deep reddish or crimson, rarely magenta or dull orange, or proximally greenish near base, distally colored as above, oblong to broadly lanceolate, often spreading from base and exposing calyces, 0–3(–5)-lobed; lobes ascending to erect, linear, short to medium length, arising near or above mid length, apex acute to obtuse. Calyces colored as bracts, 18–28 mm; abaxial clefts 5–6 mm, adaxial 8–15 mm, clefts 28–50% of calyx length, deeper than laterals, lateral 1.5–6 mm, 5–25% of calyx length; lobes long-triangular, apex acute. Corollas straight to slightly curved, 20–37 mm; tube 12–21 mm; abaxial lip sometimes exserted, beak exserted; beak adaxially green, 10–16 mm; abaxial lip green, sometimes yellow, usually reduced, protruding through abaxial cleft, sometimes a little pouched, 3-lobed, 2–6 mm, 17–45% as long as beak; teeth erect, green, whitish, or yellow, 1–1.5 mm. 2n = 48.
Phenology: Flowering (May–)Jun–Jul.
Habitat: Gravel river flats, moist thickets.
Elevation: 1200–2200 m.
Castilleja purpurascens is a species of gravelly flood plains and riverbanks at moderate elevations in the vicinity of the Kicking Horse River in Yoho National Park, British Columbia, and in immediately adjacent Alberta. While this tetraploid species may be derived from hybridization between C. miniata and C. rhexiifolia, its combination of traits is unique, and the species forms morphologically consistent populations limited to a habitat not particularly favored by either putative parent species. Very occasional hybrids are known with both C. lutescens and C. miniata.