Arabis longirostris S. Watson, Botany (Fortieth Parallel), 17. 1871; Euklisia longirostris (S. Watson) Rydberg; Guillenia rostrata Greene; Streptanthella longirostris var. derelicta J. T. Howell; Streptanthus longirostris (S. Watson) S. Watson; Thelypodium longirostris (S. Watson) Jepson

Stems often several, ascending distally, (1.2-)2-6 (-7.5) dm. Basal leaves soon withered. Cauline leaves shortly petiolate or (distal) sessile; blade lanceolate to oblanceolate, or (distal) linear, 2-5.5(-6.5) cm × 3-10(-15) mm, (attenuate to petiolelike base), margins entire, dentate to sinuate, or pinnatifid, (distal cauline (1-)1.7-5.8(-7) cm × (0.7-)1.5-4(-7) mm, base cuneate to attenuate, margins entire, apex obtuse to acute). Fruiting pedicels usually curved, rarely straight, (1-)2-5 (-7) mm. Flowers: sepals (2-)2.5-4(-5) × 0.7-1.5 mm; petals (3.5-)4-6(-7) × 0.7-1.1 mm, claw oblanceolate, 3-5 mm (longer than blade); filaments with at least dorsal pair exserted, (longest pair) 3-6 mm; anthers 0.5-1(-1.3) mm. Fruits slightly to strongly reflexed, sometimes secund, (2.5-)3.5-6(-7) cm × 1.5-2(-2.2) mm; valve apex adnate with style and replum, forming indehiscent tip, often 1-seeded; style (2-)3.5-6(-8) mm. Seeds light brown, 2-3 × 1-1.7(-2) mm; wing 0.3-0.7 mm wide. 2n = 28.

Flowering early Jan-late Jun. Roadsides, rocky areas, sandy ridges, sagebrush and creosote bush deserts, dry slopes, dry washes, decomposed granitic soil, pinyon-juniper areas, alluvial fans, chaparral, sandstone gravel and outcrops, sandstone hills and cliffs; 60-2200 m; Ariz., Calif., Colo., Idaho, Mont., Nev., N.Mex., Oreg., Utah, Wash., Wyo.; Mexico (Baja California, Sonora).

Streptanthella longirostris is most widely distributed in southern California, Nevada, and southern and central Utah, and appears to be restricted elsewhere: Colorado (Mesa, Montezuma, Montrose, San Miguel), Idaho (Butte), Montana (Carbon), New Mexico (San Juan), Washington (Franklin, Grant), and Wyoming (Fremont, Natrona, Sweetwater, Uinta).