Herbs annual or biennial, (5-)10-35(-55) cm tall, fetid, puberulent with terete papillate trichomes. Stems erect or ascending, branched above. Basal leaves with petioles 1-2(-3) cm; leaf blade (1 or)2- or 3-pinnatisect, (1.5-)3-5(-6) × (0.5-)0.7-2(-2.5) cm, glabrous except for ciliate margin; ultimate lobes oblong, entire or rarely toothed, acute. Upper cauline leaves sessile; leaf blade linear, (0.4-)1-2(-3) cm × (0.3-)0.5-2.5(-3.5) mm, sparsely pubescent, base cuneate, not auriculate, margin usually entire, ciliate, apex obtuse to subacute. Fruiting pedicels slender, divaricate, straight or slightly curved, (1.5-)2-4(-5) mm, puberulent all around. Sepals oblong, 0.5-0.9(-1) × 0.2-0.4 mm, puberulent with papillate trichomes, margin and apex white. Petals absent, sometimes rudimentary and to 0.4 mm. Stamens 2; filaments 0.7-0.8 mm; anthers ovate, 0.1-0.2 mm. Fruit broadly elliptic, (1.5-)1.8-2.5(-3) × 1.5-2(-2.3) mm, narrowly winged apically; apical notch 0.1-0.2 mm; style to 0.1 mm, included in apical notch. Seeds brown, oblong or ovate-oblong, 1-1.5 × 0.6-0.7 mm, wingless, finely papillate; cotyledons incumbent. Fl. and fr. May-Jul. 2n = 16, 32*.

Lepidium ruderale was recorded in FRPS from Gansu, Henan, Hubei, Jilin, Liaoning, Ningxia, Qinghai, Shaanxi, and Shandong. The present authors have seen no material from these provinces, and it is likely that these records are based on misidentified plants of L. apetalum. The former is a fetid plant, puberulent with slender trichomes, with basal leaves (1 or)2- or 3-pinnatisect, cauline leaves nonauriculate, and fruiting pedicels terete, puberulent all around with slender trichomes. By contrast, L. apetalum is a nonfetid plant, puberulent with capitate or clavate trichomes, with basal leaves pinnatifid, cauline leaves often subauriculate, and fruiting pedicels slightly flattened or obscurely winged, puberulent almost always only adaxially.

Sandy soil, pastures; 300-1100 m. Xinjiang [India, Kazakhstan, Kyrgyzstan, Mongolia, Russia, Tajikistan, Turkmenistan, Uzbekistan; SW Asia, Europe; introduced in North America].