40. Lepidium thurberi Wooton, Bull. Torrey Bot. Club. 25: 259. 1898.
Annuals; pubescent, (trichomes cylindrical, to 1 mm, and much shorter, clavate ones). Stems often simple from base, erect, branched (several) distally, (0.8)1.2-4.9(-6) dm. Basal leaves (often withered at anthesis); rosulate; petiole 1-3 (-4.5) cm; blade pinnatifid (lobes oblong to ovate or lanceolate), (1.4-)2.2-7(-10) cm, margins (of lobes) dentate-sinuate. Cauline leaves shortly petiolate; 1.5-6 cm × 6-25 mm, base not auriculate, margins (of lobes) entire or dentate. Racemes considerably elongated in fruit; rachis pilose, trichomes straight, cylindrical (to 1 mm) with much smaller, clavate ones, sometimes one type present. Fruiting pedicels divaricate-ascending to horizontal, straight or slightly recurved, (terete), 4-8(-10) × 0.2-0.3 mm, puberulent or pilose adaxially. Flowers: sepals suborbicular to broadly ovate, 1-1.6 × 0.7-1 mm; petals white, broadly obovate to suborbicular, 3-4 × 1.2-2.2 mm, claw 0.7-1.3 mm; stamens 6; filaments (median pairs) 1-1.6 mm, (glabrous); anthers 0.4-0.5 mm. Fruits broadly ovate to orbicular, 2-2.9 × 2-2.8 mm, apically winged, apical notch 0.1-0.2 mm deep; valves thin, smooth, not veined, glabrous; style 0.3-0.8 mm, exserted beyond apical notch. Seeds ovate-oblong, 1.3-1.6 × 0.8-1.1 mm.
Flowering Apr-Aug. Salt flats, mesquite and creosote bush communities, playas, stream banks, sandy deserts, washes, clay bottoms, bluffs, gravelly granitic sand, grasslands, alluvial fans, roadsides, silty terraces, washes, gravelly flats; 600-1800 m; Ariz., Calif., N.Mex.; Mexico (Chihuahua, Coahuila, Sonora).