Cat. N. Amer. Pl., 7. 1898.
Plants simple, branched, or multiple stems from host attachment, 5–45 cm, stout, sometimes slender, base usually enlarged. Roots usually relatively conspicuous (often forming an irregular mass), slender, branched. Leaves numerous, appressed; blade ± lanceolate to broadly ovate, 6–12 mm, margins entire, apex acute or obtuse, surfaces sometimes glandular-pubescent. Inflorescences spikelike racemes, purple, usually branched, densely glandular-pubescent, sometimes appearing canescent; flowers numerous; bracts erect to reflexed, lanceolate to linear, 5–12 mm, apex acuminate, obtuse, or acute, glandular-pubescent. Pedicels 0–30 mm, much shorter than plant axis; bracteoles 2. Flowers: calyx dark purple or lavender, weakly bilaterally symmetric, 8–12 mm, deeply divided into 5 lobes, lobes lanceolate-acute to -attenuate, densely glandular-pubescent; corolla 15–32 mm, tube purple or lavender, rarely white, tinged with purple, constricted above ovary, bent forward, ± glandular-pubescent; palatal folds prominent, yellow, densely pubescent; lips dark purple to lavender, with darker purple veins, abaxial lip spreading or slightly reflexed, 3–9 mm, lobes oblong-lanceolate to narrowly ovate, apex acute, often with apiculate tooth, adaxial lip erect, reflexed, or revolute, 6–10 mm, lobes ± triangular, rarely truncate, apex acute, often with apiculate teeth; filaments glabrous, anthers included, glabrous, sparsely villous, pubescent, or tomentulose along sutures, usually also with inconspicuous stalked glands (these minute, appearing peglike under magnification). Capsules ovoid, 6–12 mm. Seeds 0.2–0.5 mm.
Ariz., Calif., N.Mex., Nev., Tex., n Mexico.
Subspecies 3 (3 in the flora).
The hosts for Orobanche cooperi are shrubs of Ambrosia and Viguiera (Asteraceae).
L. R. Heckard and T. I. Chuang (1975) mentioned an undescribed polyploid variant (2n = 96) with smaller, shorter-lobed corollas and peltate, bowl-shaped stigmas occurs on the same hosts in southern California.
|1||Corollas 15–18(–22) mm, lips 3–6 mm, adaxial lips reflexed or revolute; anthers glabrous or tomentulose from pollen sacs, stalked glands often few on dorsal surfaces or absent; Chihuahuan Desert.||Orobanche cooperi subsp. palmeri|
|1||Corollas (15–)18–32 mm, lips 5–10 mm, adaxial lips erect or reflexed; anthers glabrous, sparsely villous, or pubescent, stalked glands present on dorsal surfaces, sometimes obscure, rarely absent; Sonoran Desert and adjacent portions of California and Nevada.||> 2|
|2||Corollas (15–)18–22 mm, adaxial lips erect, lobes with or without apiculate teeth.||Orobanche cooperi subsp. cooperi|
|2||Corollas 22–32 mm, adaxial lips erect or reflexed, lobes with apiculate teeth.||Orobanche cooperi subsp. latiloba|