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).
Duration: Annual Nativity: Native Lifeform: Forb/Herb General: Annual or biennial under ideal conditions with erect, ascending, freely branched stems 10-60 cm tall, stems hirsute-canescent to pilose throughout, longer hairs obviously flattened, shorter ones usually papilliferous or clavate. Leaves: Lower leaves oblanceolate in outline, 3-7.5 cm long, 1-1.5 cm wide, pinnatifid into 3-8 pairs of more or less lobed or dissected segments, ultimate divisions linear to obovate, acute, or apiculate; cauline leaves reduced but similar to lower leaves. Flowers: Many flowered raceme, elongating at 1.5-2 cm in fruit; slender pedicels, spreading 6-9 mm long in fruit, slightly flattened, pilosulous along margins; sepals broadly ovate, white, 1-1.5 mm long, petals white 2-3 mm long, glabrous filaments.February-September. Fruits: Silicles ovate to suborbicular 2-2.5 mm wide, 2-3 mm long, very shallowly and narrowly notched, glabrous. Ecology: Found in waste places, roadsides, along washes, and disturbed areas; below 5,000 ft (1524 m); flowers February-September. Distribution: s CA, AZ, NM; south to n MEX. Notes: Distinct by being an annual that is not very branched from the base (as in lasiocarpum); small to long, flattened or sometimes straight hairs all over; basal leaves in a rosette and pinnately lobed; stem leaves entire to dentate; inflorescences which become highly elongated in fruit; white petals; fruiting pedicels diverging not appressed and not flattened; style excserted from fruit notch and hairless fruits. Ethnobotany: Papago gathered seeds, winnowed them, parched, dried, cooked, and used for food. Etymology: Lepidium is from Greek lepidion, meaning little scale, a reference to the shape of the fruits, thurberi is named for Dr. George Thurber (1821-1890) a member of the Mexican Boundary Survey. Synonyms: None Editor: SBuckley 2010, FSCoburn 2015