5. Caulanthus cooperi (S. Watson) Payson, Ann. Missouri Bot. Gard. 9: 293. 1923; Thelypodium cooperi S. Watson, Proc. Amer. Acad. Arts 12: 246. 1877; Guillenia cooperi (S. Watson) Greene, Leafl. Bot. Observ. Crit. 1: 228. 1906. TYPE: United States, California, San Bernardino Co., near Fort Mohave, 1861, J. G. Cooper s.n. (holotype, GH!).

Herbs, annual, puberulent or glabrous, glaucous. Stems 1–8 dm, erect to ascending, often flexuous, weak and often tangled with desert shrubs, often branched above, glabrous or puberulent with simple and subappressed 2-rayed trichomes. Basal leaves rosulate; petiole 0.3–2.5 cm; blade oblanceolate to spatulate, 0.7–6 x 0.2–2.7 cm, glabrous, margin coarsely dentate or somewhat pinnatifid, rarely entire; middle cauline leaves sessile, lanceolate or oblong, 1.5–7.5 x 0.5–2 cm, gradually reduced in size upwards, glabrous, base amplexicaul to sagittate, margin dentate or entire. Racemes without a terminal cluster of sterile flowers, ebracteate, lax, elongated in fruit; fruiting pedicels reflexed, 1–4.5 mm, glabrous or rarely puberulent. Sepals purplish or yellow-green, narrowly lanceolate, 3–6.5 ´ 0.8—1.5 mm, erect, equal, not keeled; petals yellow-green to purplish, often with purple veins, 4.5–9 mm; blade 2–3 x 0.7–1.5 mm, not crisped; claw narrowly oblong-oblanceolate, 2.5–7 x 1–1.5 mm; filaments slightly tetradynamous, free, median pairs 2–4.5 mm, lateral pair 1.5–3.5 mm; anthers oblong, 1.5–2 mm; ovules 24–48 per ovary. Fruits 2–6 cm ´ 1.5–2.5 mm, reflexed or rarely divaricate, terete, often subfalcate; valves glabrous or puberulent, with a prominent midvein; style 0.2–2.7 mm; stigma slightly 2-lobed. Seeds 1–2 x 1–1.2 mm; cotyledons entire.

Flowering (Jan–)Feb–Mar.

Habitat: desert shrubs, woodlands.

Elevation: 600–2300 m.

Distribution: Mexico (Baja California), United States (W Arizona, S and C California, Nevada).