Syst. Bot. 16: 658. 1991.
Herbs, annual, 0.45–5.2 dm; with a slender taproot or branched root system. Stems solitary, erect, unbranched or with few upright branches, hairs spreading, long, soft, mixed with shorter, eglandular and glandular ones. Leaves green to brown, proximal linear, distal lanceolate, 0.7–4 (–8) cm, not fleshy, margins plane, flat, 0–3 (–5) -lobed, apex acuminate; lobes ascending-spreading, very long linear, apex acute. Inflorescences 2–25 × 1–3 cm; bracts green, sometimes proximally green, distally dull brownish to deep purplish brown, lanceolate to narrowly ovate or ovate, (3–) 5–7 (–9) -lobed; lobes ascending to erect, linear or narrowly lanceolate, long, proximal lobes arising below mid length, apex acute to acuminate. Calyces green to brownish, margins sometimes deep purple or brown, 6–12 mm; abaxial and adaxial clefts 2–5 mm, 33–50% of calyx length, deeper than laterals, lateral 2–3.5 mm, 30–40% of calyx length; lobes linear to narrowly lanceolate, apex acute to acuminate. Corollas straight to ± curved distally, 12–20 mm; tube 9–14 mm; abaxial lip and beak exserted; beak adaxially white or pale yellowish, 3.5–5 mm, inconspicuously puberulent; abaxial lip white or yellow, 3 small redbrown dots near base, inflated, pouches 3, 2–4 mm wide, 2 mm deep, 2–4 mm, 50–70% as long as beak; teeth erect, white or yellow, 0.5–1 mm. Stigmas included within beak. 2n = 24, 48.
Phenology: Flowering Feb–Sep.
Habitat: Moist flats, vernal pools, springs, damp meadows and ditches, riparian zones, sometimes over serpentine.
Elevation: 200–2800 m.
B.C., Calif., Idaho, Nev., Oreg., Wash.
Castilleja tenuis is restricted to the east side of the Cascade Range in British Columbia and Washington and also occurs west of the Cascade-Sierra axis in the more arid terrain of California and Oregon. Plants in the Umpqua and Willamette valleys of western Oregon are often taller, more robust, and with slightly larger flowers than is typical in other regions. There are two color forms, with white or yellow corollas, but most individual populations are consistently unicolored. More investigation is needed to determine if corolla color is influenced by genetic and/or environmental factors. There is some evidence (T. I. Chuang and L. R. Heckard 1982) that the colors are correlated to chromosome number, with the white-flowered plants being diploid, while the yellow-flowered plants are tetraploid; however, there are exceptions. D. D. Keck (1927) cited some evidence for seasonal change, with yellow flowers occurring early, replaced with white flowers later in the season. However, no unequivocal evidence exists to support this hypothesis, and the apparently complete absence of yellow-flowered plants in Oregon makes this an unlikely explanation. Cropping by grazing animals results in occasional plants that branch. Plants with slightly curved corolla beaks were described as Orthocarpus falcatus but have no geographic integrity or taxonomic significance. Castilleja tenuis was collected as a waif in Skagway, Alaska, a century ago.