Bull. Torrey Bot. Club 100: 87, fig. 3. 1973.
Herbs, perennial, 1.1–3.9 dm; from a woody caudex; with numerous, thickened roots. Stems few to several, ascending to erect, unbranched, hairs moderately dense, often retrorse, short, ± stiff, stipitate-glandular distally only in inflorescence. Leaves appressed-ascending, green to purplish, linear to narrowly lanceolate, distal sometimes broadly lanceolate, (1–)2.5–4(–5.5) cm, not fleshy, margins plane, involute, 0(–5)-lobed, apex rounded to acuminate; lobes ascending, linear to narrowly lanceolate, apex acute. Inflorescences 2–7 × 1.5–2 cm; bracts proximally pale green to pale yellow-green, distally pale to bright yellow or cream, rarely pale orange, elliptic, narrowly ovate, elliptic-oblong, broadly lanceolate, or ovate, (0–)3(–5)-lobed; lobes ascending or spreading, narrowly lanceolate, short, arising near tip on distal bracts, central lobe apex rounded to truncate, lateral ones acute to rounded. Calyces proximally green to yellowish, distal 1/2 yellow, (16–)18–25 mm; abaxial and adaxial clefts (8–)9.5–12.5 mm, 50% of calyx length, deeper than laterals, lateral 0.5–5(–6) mm, 5–20% of calyx length; lobes lanceolate to ovate, apex acute to obtuse. Corollas straight, 17–25 mm; tube 9–13 mm; beak exserted, adaxially green, 6–8(–12) mm, margins red or reddish brown, short-hairy; abaxial lip green, reduced, sometimes exserted, 1.5–2 mm, 10–15% as long as beak, glabrous; teeth erect, green, 0.5–1.5 mm.
Phenology: Flowering Jun–Aug.
Habitat: Meadows with sagebrush, openings in spruce-fir forests.
Elevation: 2900–3400 m.
Castilleja aquariensis is endemic to the Aquarius Plateau in the mountains of south-central Utah. Its meadow habitats were severely degraded by livestock grazing, and at one time the species was a candidate for listing under the Endangered Species Act of the United States. It is still a species of management concern.
Castilleja aquariensis is in the Center for Plant Conservation’s National Collection of Endangered Plants.