Mem. New York Bot. Gard. 1: 356. 1900.
Herbs, perennial, (1–) 2.5–6 (–8) dm; from a woody caudex; with a taproot. Stems few to several, erect or ascending, unbranched, sometimes branched, proximally glabrous to glabrate, distally sparsely hairy, hairs spreading, ± long, soft, eglandular, sometimes stipitate-glandular. Leaves green or purple-tinged, linear, narrowly to broadly lanceolate, oblong, or ovate, 3–6 (–7) cm, not fleshy, margins plane, flat to slightly involute, prominently veined, 0 (–3) -lobed, apex acute to rarely obtuse; lobes ascending or spreading, linear to filiform, much smaller than mid-blade, short, apex acute. Inflorescences 2.5–15 × 1.5–4.5 cm; bracts pink-purple, red-purple, purple, or crimson throughout, rarely reddish, yellowish, or white throughout, or proximally greenish, dull brownish purple, or deep purple, distally colored as above, broadly lanceolate to ovate or obovate, (0–) 3–5 (–7) -lobed; lobes ascending to erect, linear or lanceolate-acuminate, short, arising near or above mid length, central lobe apex obtuse to broadly rounded, lateral ones acute to sometimes rounded. Calyces proximally green, purplish, or whitish, distally colored as bracts, 15–25 mm; abaxial and adaxial clefts 8–12 (–15) mm, 40–50% of calyx length, deeper than laterals, lateral 2–5 (–8) mm, 15–25 (–30) % of calyx length; lobes oblong to triangular or ovate, apex obtuse to rounded, sometimes acute. Corollas straight, 15–30 (–36) mm; tube (11–) 12–22 (–24) mm; beak exserted, adaxially green, yellow, or tinged with red, 7–12 mm; abaxial lip deep green, reduced, 1.5–3.5 mm, to 33% as long as beak; teeth incurved, green or white, 0.5–2 mm. 2n = 24, 48, 96.
Phenology: Flowering (Mar–)May–Sep.
Habitat: Moist meadows, open forests, slopes and ridges, sun or shade, subalpine to alpine.
Elevation: 1800–4000 m.
Alta., B.C., Colo., Idaho, Mont., N.Mex., Oreg., Utah, Wash., Wyo.
Castilleja rhexiifolia is a characteristic and common paintbrush in the Rocky Mountains region, from central Alberta to northern New Mexico. Disjunct populations also occur in northeastern Oregon, in the Blue, Ochoco, and Wallowa mountains, as well as near the summit of Abercrombie Mountain in the Selkirk Mountains of northeastern Washington. The inflorescence colors are variable. Typical plants are red-purple. However, many other shades of pink-white, pink-purple, and crimson are common as well. Many populations contain a wide range of color variants. Intergradation is occasionally seen with C. miniata, C. occidentalis, and C. septentrionalis. However, for the most part, these four species remain distinct, and their ranges are not entirely overlapping. In the Wallowa Mountains, a recurrent and variable hybrid form between C. chrysantha and C. rhexiifolia was described as C. wallowensis Pennell. In the north Cascade Range of Washington, plants of C. elmeri with crimson inflorescences are sometimes identified as C. rhexiifolia. In Glacier National Park, Montana, in the vicinity of Logan Pass, C. rhexiifolia frequently hybridizes with C. occidentalis, creating a number of hybrid morphologies. Both of the parents are common in the area. Similar hybrids are also found in the Canadian Rocky Mountains.