Rep. U.S. Mex. Bound. 2(1): 118. 1859.
Herbs or subshrubs, perennial, 1.3–5 dm; from a woody caudex; with a taproot. Stems few-to-many, ascending to erect, unbranched or branched, with short, leafy axillary shoots, moderately lanate, hairs prostrate to spreading, whitish, unbranched, short, fairly soft, eglandular. Leaves green, linear to narrowly lanceolate, (0.8–) 3–5 cm, not fleshy, margins plane, strongly involute, 0–3 (–5) -lobed, apex acute to rounded; lobes spreading, linear, short, apex acute. Inflorescences 5–20 × 0.5–2.5 cm; bracts proximally dull brownish to deep greenish purple, distally red, red-orange, or orange, lanceolate or oblong to obovate, deeply 3 (–5) -lobed; lobes ascending, linear to lanceolate, long, arising below mid length, central lobe apex rounded to obtuse, others acute. Calyces colored as bracts, (10–) 13–19 mm; abaxial and adaxial clefts 4–8 (–11) mm, 33–50% of calyx length, deeper than laterals, lateral 5–7 mm, ca. 25% of calyx length; lobes linear to lanceolate, apex acute. Corollas straight or slightly curved, 12–20 mm; tube 13–15 mm; beak exserted or ± equal to calyx, adaxially pale green, 8–11.5 mm; abaxial lip green or red-violet, inconspicuous, slightly pouched, 1.5–2 mm, ca. 10–20% as long as beak; teeth incurved, pink to pale-yellow or deep green, 1 mm.
Phenology: Flowering Jun–Oct.
Habitat: Dry Chihuahuan grasslands.
Elevation: 1300–1700 m.
N.Mex., Mexico (Sonora)
In the United States, Castilleja tomentosa is known from a number of recently discovered populations in and near the southern Animas Valley, Hidalgo County, where it is found in Bouteloua gracilis and Sporobolus airoides grasslands. All known populations are small, and this species should be considered globally endangered. The only recorded Mexican station was the type locality from 1851 near Mabibi in adjacent northern Sonora. A. Eastwood (1909) believed C. tomentosa was a synonym of C. integra, but that species has mostly entire bracts, while the bracts of C. tomentosa are deeply lobed; the two also have different patterns of coloration and pubescence. T. I. Chuang annotated the holotype sheet of C. tomentosa as C. lanata, but C. tomentosa calyces have fairly deep lateral lobes, unlike the emarginate to very shallowly notched lobes of C. lanata.
"arising" is not a number.