1. Hornungia procumbens (Linnaeus) Hayek, Repert. Spec. Nov. Regni Veg. Beih. 30: 480. 1925.
Lepidium procumbens Linnaeus, Sp. Pl. 2: 643. 1753; Capsella elliptica C. A. Meyer; C. procumbens (Linnaeus) Fries; Hutchinsia procumbens (Linnaeus) Desvaux; Hymenolobus divaricatus Nuttall; H. erectus Nuttall; H. procumbens (Linnaeus) Nuttall; Noccaea procumbens (Linnaeus) Reichenbach; Thlaspi procumbens (Linnaeus) Wallroth
Plants glabrous throughout or puberulent, trichomes usually minutely forked, some simple. Stems (0.2-)0.5-2.2(-3) dm. Basal leaves: petiole (0.2-)0.5-1.2(-2) cm; blade obovate, oblanceolate, or oblong, (0.2-)1-2.5(-4) cm × (1-)5-11(-16) mm, base cuneate or attenuate, apex acute or obtuse. Cauline leaves (distal) subsessile; blade similar to basal (smaller distally). Racemes few- to several-flowered (rachis straight or slightly flexuous in fruit). Fruiting pedicels 3-8(-12) mm. Flowers: sepals 0.6-1.1 × 0.4-0.6 mm; petals 0.6-1.2 × 0.3-0.6 mm; filaments (white), 0.5-1 mm; anthers ca. 0.1 mm. Fruits (0.2-)0.3-0.4(-0.5) cm × (1-)1.4-2.2 mm, apex subtruncate to slightly emarginate. Seeds 0.5-0.6 × 0.3-0.4 mm. 2n = 12, 24.
Flowering Feb-Jul. Deserts, meadows, shade of bushes, disturbed habitats, waste places, saline banks, salt marshes, sagebrush plains, alkaline flats, slopes; 0-2600 m; introduced; B.C., Man., Nfld. and Labr. (Nfld.), Sask.; Calif., Colo., Idaho, Mont., Nev., Oreg., Utah, Wash., Wyo.; Europe; Asia; n Africa; introduced also in Mexico, South America, s Africa, Australia.
Hornungia procumbens is highly variable, especially in fruit size and shape, number of seeds per fruit, indumentum, plant size, and shape and number of leaf divisions. Many of its morphological extremes were recognized at specific and infraspecific ranks, and more than 40 synonyms exist.