Biennials or perennials; (short-lived); glaucous, glabrous (except petioles). Stems branched distally, 2-10 dm. Basal leaves: petiole (0.9-)1.4-3(-4.5) cm, ciliate; blade usually oblanceolate to oblong or lanceolate, rarely ovate or elliptic, (2.8-)3.5-8.8(-11) cm × (7-)10-25(-35) mm, margins often entire or repand, sometimes sinuate. Cauline leaves (ascending); sessile; blade lanceolate to oblong, 1.8-4.5(-6) cm × 5-16(-24) mm, (base amplexicaul to strongly auriculate), margins entire. Racemes lax, slightly elongated in fruit, (flower buds oblong-linear). Fruiting pedicels horizontal to divaricate, usually straight, rarely slightly incurved, slender, (2.5-)3-5.5(-6.5) mm, slightly flattened at base. Flowers: sepals erect, linear-oblong, 5-7(-8) × (0.8-) 1-1.5(-1.8) mm; petals dark purple, spatulate to oblanceolate, (6.6-)7.5-10(-11.5) × 1-1.8(-2) mm, margins not crisped, claw differentiated from blade, [slender, (3-)3.5-5(-5.5) mm, narrowest at base]; nectar glands confluent, subtending bases of stamens; filaments subequal, (4.5-)6-9(-10) mm; anthers exserted, linear to narrowly oblong, 2.5-4(-4.5) mm, circinately coiled; gynophore (1-)2.5-6(-7.5) mm. Fruits divaricate to ascending, torulose, straight or slightly incurved, terete, (2-)2.4-5(-6.5) cm × 0.7-1(-1.3) mm; ovules 44-58 per ovary; style usually cylindrical, rarely subclavate, 0.5-1.5(-2) mm. Seeds 0.7-1.5 × 0.5-0.8 mm.

Flowering May-Jul. Shady slopes and canyons, pinyon-juniper and oak woodland communities, stream beds, streamsides; of conservation concern; 700-1000 m; Oreg.

Thelypodium eucosmum is known only from Baker, Grant, and Wheeler counties. It is in the Center for Plant Conservation’s National Collection of Endangered Plants.