Annuals; usually glabrous throughout (sometimes stem bases pubescent). Stems unbranched or branched distally, 2.8-13 dm. Basal leaves not seen. Cauline leaves (shortly petiolate or sessile); blade usually linear to linear-lanceolate, rarely oblanceolate, 2.5-16 cm × 2-7(-20) mm, (smaller distally), base not auriculate, margins entire. Racemes ebracteate. Fruiting pedicels divaricate-ascending, (straight), 3-10 mm. Flowers (slightly zygomorphic, horizontal to pendent); calyx campanulate; sepals purple, lanceolate, 7-11 mm, not keeled; petals deep purple to magenta or whitish (with purple veins), 13-20 mm, blade 7-12 × 1-4 mm, margins not crisped, claw 5-12 mm, (strongly recurved); stamens in 3 unequal pairs; filaments: abaxial pair (connate less than 1/2 their length), 8-14 mm, lateral pair 4-7 mm, adaxial pair (connate ca. 3/4 their length), 7-10 mm; anthers: abaxial and lateral pairs fertile, 2-3 mm, adaxial pairs sterile, 1-1.5 mm; gynophore 0.3-3 mm. Fruits divaricate-ascending, smooth, straight or slightly curved inwards, flattened, 3.7-11.2 cm × 1.5-2 mm; valves each with prominent midvein; replum straight; ovules 90-120 per ovary; style 0.3-1.5 mm; stigma subentire. Seeds broadly ovoid, 1.5-1.8 × 1-1.3 mm; wing 0.1-0.25 mm, continuous.

Flowering May-Jun. Sandy soils of prairies, open glades in woods, grassy roadsides; 100-800 m; Ark., Kans., La., Okla., Tex.

Streptanthus hyacinthoides is widespread in eastern Texas and central and northwestern Oklahoma; in Arkansas it is restricted to Nevada and Ouachita counties; in Kansas to Barber and Comanche counties; and in Louisiana to Bienville, Caddo, Natchitoches, and Winn parishes.