Annuals; (glaucous), glabrous throughout . Stems unbranched or branched basally, 0.3-1.7 (-2.8) dm. Basal leaves (soon withered); not rosulate; shortly petiolate; blade (succulent, mottled), obovate to ob-lanceolate, 0.5-2 cm, margins coarsely dentate. Cauline leaves: blade lanceolate, 0.5-2.5 cm × 1-7 mm (smaller distally), base auriculate, margins entire or dentate (entire distally). Racemes ebracteate (lax, sometimes secund). Fruiting pedicels divaricate-ascending, 1-2.5(-4) mm. Flowers: calyx urceolate; sepals (erect) reddish purple, (ovate), 3-5 mm, keeled, (apex spreading); petals whitish (abaxial pair with purplish veins, adaxial pair purple), 5-8 mm, blade 2-3 × 1-1.5 mm, margins not crisped, claw 3-4 mm; stamens in 3 unequal pairs; filaments: abaxial pair (connate to middle), 3-4 mm, lateral pair 1.5-2.5 mm, adaxial pair (completely connate, not recurved), 5-6 mm; anthers: abaxial and lateral pairs fertile, 1.4-1.7 mm, adaxial pairs sterile, 0.3-0.5 mm; gynophore 0.3-0.7 mm. Fruits divaricate-ascending, slightly torulose, straight to slightly curved, slightly flattened, 1.3-3 cm × 1-1.5 mm; valves each with obscure midvein; replum straight; ovules 12-22 per ovary; style 0.2-0.8 mm; stigma entire. Seeds oblong, 1.3-2 × 0.8-1.2 mm; wing 0.1-0.3 mm wide distally, (narrower at margin, rarely absent). 2n = 28. Flowering May-Jun. Serpentine barrens and outcrops in chaparral; of conservation concern; 100-600 m; Calif. Streptanthus batrachopus is known from Mt. Tamalpais, Marin County.