Contr. Dudley Herb. 5: 99. 1958.
Plants simple, rarely branched, 5–12 (–18) cm, usually slender, base sometimes enlarged. Roots usually inconspicuous (sometimes forming an irregular mass), slender, unbranched or with short bifurcations. Leaves few to several, appressed; blade broadly lanceolate or ovate, 5–10 mm, margins entire or slightly erose, apex acute or obtuse, surfaces often glandular-pubescent. Inflorescences racemelike to elongate corymbs or short racemes (sometimes corymbose), rose, pink, purple, or white, simple, densely glandular-pubescent; flowers numerous (rarely 10 or fewer in depauperate plants); bracts slightly reflexed, narrowly lanceolate or almost linear, 7–11 mm, apex acute, glandular-pubescent. Pedicels 3–20 mm proximally, 0 mm distally, shorter than plant axis; bracteoles 2. Flowers: calyx lavender, pink, white, or yellow, sometimes burgundy, ± radially symmetric, 12–24 mm, deeply divided into 5 subequal (reflexed or contorted) lobes, lobes linear-subulate, densely glandular-pubescent; corolla (15–) 18–34 mm, tube white to grayish white, pale-pink to pink, or pale-purple to purple, rarely brick-red, sometimes with darker-pink to purple veins, slightly constricted above ovary, bent forward, glandular-pubescent or glabrate; palatal folds prominent, yellow, glabrous (with blisterlike swellings); lips white to ± pink, pale-purple to purple, brick-red, or pinkish red, sometimes with darker-pink to purple veins or internally darker, abaxial lip spreading, 5–9 mm, lobes oblong to oblong-lanceolate, apex acute or rounded, adaxial lip erect or reflexed, 5–9 mm, lobes oblong, apex rounded, truncate, or emarginate, rarely acute; filaments glabrous, anthers included, tomentose, sometimes glabrous (subsp. mutabilis). Capsules ovoid to oblong-ovoid, 5–13 mm. Seeds 0.3–0.5 mm.
Alta., B.C., Man., Ariz., Calif., Idaho, Mont., N.Mex., Nev., Oreg., Utah, Wash., Wyo.
Subspecies 2 (2 in the flora).
The range of Orobanche corymbosa includes the Great Basin Desert, Intermountain Region, Columbia Plateau, and contiguous areas. The two subspecies are sympatric through most of the geographic range of the species. Areas of sympatry exist with several other species of Orobanche: in the west with O. californica; in the north and east with O. ludoviciana; and in the south with O. arizonica and O. multiflora. Subspecies mutabilis tends to produce more racemose inflorescences, while subsp. corymbosa typically produces more compact corymbose inflorescences. This suggests a genetic affinity between O. corymbosa and members of the O. californica and O. ludoviciana groups. The southern members of subsp. corymbosa in California and Nevada appear to intergrade with O. californica across the Sierra Nevada. However, there are exceptional individuals in every population, so seasonal weather may cause variations in plant morphology.
Inflorescence differences could also be associated with the ploidy differences reported in Orobanche corymbosa (L. R. Heckard and T. I. Chuang 1975). Ploidy and morphological instability may indicate significant introgression or a hybrid origin of O. corymbosa.
Both subspecies share a somewhat ampliate corolla tube, which is a good field character for this species when compared with species with which it has an overlapping range. Orobanche corymbosa is parasitic on species of Artemisia (Asteraceae), principally A. tridentata, but has occasionally been reported on Iva (Asteraceae) and Atriplex and Sarcobatus (Chenopodiaceae).
|1||Inflorescences simple corymbs or short corymbose racemes; calyces (13–)15–24 mm, equal to or shorter than corollas; corollas glandular-pubescent; anthers tomentose.||Orobanche corymbosa subsp. corymbosa|
|1||Inflorescences short racemes or racemelike to elongate corymbs; calyces 12–18 mm, sometimes equal to or longer than corollas; corollas glabrate or slightly glandular-pubescent; anthers tomentose or glabrous.||Orobanche corymbosa subsp. mutabilis|