Novon 12: 322. 2002.
Annuals or biennials; caudex simple or branched, (relatively small, cespitose); densely pubescent, trichomes (spreading, sessile or short-stalked), 5–7-rayed, rays distinct and simple, (tuberculate, finely tubercled with a U-shaped notch on one side). Stems simple or few to several from base, erect or decumbent, (rarely branched, usually leafy), to 4 dm. Basal leaves: blade lyrate-pinnatifid, 1–7 cm, margins entire or shallowly dentate. Cauline leaves (sessile or shortly petiolate); blade narrowly obovate to elliptic, 0.5–6 cm, margins entire, repand, or shallowly dentate. Racemes dense, (elongated in fruit, often subtended by distal cauline leaves). Fruiting pedicels (usually divaricate-spreading, straight or slightly curved, delicate, sometimes drooping, especially on herbarium specimens), 7–10 mm, (somewhat rigid). Flowers: sepals elliptic, 3.7–7.2 mm, (lateral pair somewhat cucullate, median pair thickened apically); petals (yellow to orange-yellow), obovate to obdeltate, (4.5–)7–10(–11) mm, (tapering to short claw, apex often emarginate). Fruits (sessile or substipitate), globose or broadly obovate, not inflated, 4–6 mm, (smooth); valves (not retaining seeds after dehiscence), glabrous; replum as wide as or wider than fruit; ovules 8–16 per ovary; style 2–5 mm. Seeds flattened. 2n = 14.
Phenology: Flowering Mar–May.
Habitat: Sandy, granitic, or calcareous soils, sandy ledges, limestone outcrops, rocky prairies, uplands
Elevation: 30-400 m
Alyssum densiflorum (A. Gray) Kuntze (1891), not Desfontaines (1808) is an illegitimate name, sometimes found in synonymy with Physaria densiflora.