Biennials or perennials; (short-lived). Trichomes of leaves 2-4(-7)-rayed. Stems erect, unbranched or branched distally, 0.4-9(-13) dm. Basal leaves: blade (somewhat fleshy), linear-oblanceolate, 3.5-15.5 cm × 2-9 mm, base attenuate, margins entire or obscurely dentate, apex acute. Cauline leaves: blade (oblanceolate), margins entire. Racemes considerably elongated in fruit. Fruiting pedicels divaricate to divaricate-ascending, stout, slightly narrower than fruit, 4-10(-13) mm. Flowers: sepals oblong to linear-oblong, 7.5-11(-13) mm, lateral pair slightly saccate basally; petals bright yellow, broadly obovate to suborbicular, 14-24 × 6-11(-14) mm, claw 8-14 mm, apex rounded; median filaments 8.5-12 mm; anthers linear, 3-4 mm. Fruits spreading, narrowly linear, straight, not torulose, (2-)3.5-12 cm × 1.5-3.5 mm, latiseptate, not striped; valves with prominent midvein, pubescent outside, trichomes 2-4-rayed, glabrous inside; ovules 50-86 per ovary; style cylindrical, stout, 0.3-1.5 (-2) mm, sparsely pubescent; stigma slightly 2-lobed, lobes as long as wide. Seeds oblong, 1.5-3 × 1-1.8 mm; winged distally (narrowly so around). 2n = 36.

Flowering Mar-Apr. Sand dunes; of conservation concern; 0-50 m; Calif.

Erysimum ammophilum is restricted to coastal and nearby sand dunes of Monterey and Santa Cruz counties.