Fl. Rocky Mts., 364. 1917.
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.
Phenology: Flowering early Jan-late Jun.
Habitat: 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
Elevation: 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).