Thlaspi parviflorum A. Nelson, Bull. Torrey Bot. Club 27: 265. 1900

Biennials or perennials; (short- lived, rarely cespitose, glau-cous). Stems simple or 2 from base (rarely several), erect or ascending, (0.7-)1-2.5(-3.2) dm, unbranched or branched distally. Basal leaves (soon withered; subrosulate); petiole (0.2-)0.4-1.4(-2) cm; leaf blades oblanceolate to spatulate, 0.3-1.5(-1.9) cm × 2-9 mm, base cuneate, margins entire or repand, apex obtuse. Cauline leaves 4-10(-12); blade ovate or suboblong, 0.5-2(-2.3) cm × 2-7(-8) mm, base minutely auriculate, margins entire, apex obtuse to subacute. Racemes (1-)2-13(-17) cm. Fruiting pedicels horizontal, straight, (2-)2.5-5.5(-8) mm. Flowers: sepals (1-)1.3-1.8(-2.2) × 0.4-0.7 mm, (margins white); petals white, 2-2.8(-3.6) × 0.6-1.2 mm, (erect), not flaring between blade and claw, apex obtuse; filaments 1-2.2 mm; anthers ca. 0.3 mm. Fruits not winged or, rarely, narrowly winged apically, obovate, (3.5-)5-7 × 2-3.5 mm, base cuneate, apex obtuse, truncate, or retuse; ovules 4-12 per ovary; style (0.2-)0.3-0.5(-0.6) mm. Seeds golden brown, 0.8-1.2 mm, smooth. 2n = 14.

Flowering May-Jul. Meadows, sagebrush, limestone cliffs and outcrops, dry grassy slopes and ridges; 1200-2800 m; Idaho, Mont., Wyo.

Noccaea parviflora is readily distinguished from the other North American members of the genus by the smaller size of its flowers, fruits, and seeds. It is restricted to central Idaho, adjacent Montana, and northwestern Wyoming.