Syst. Nat. ed. 10, 2: 1130. 1759.
Annuals; canescent throughout, trichomes appressed, 6–10-rayed, mixed with simple and forked on pedicels and sepals. Stems simple or few to several from base, erect, ascending, or decumbent, (unbranched or branched distally), 0.5–3.5(–5) dm. Cauline leaves subsessile or (proximal) shortly petiolate; blade usually narrowly oblanceolate to linear, sometimes spatulate or obovate, 3–4(–4.5) cm × (0.5–)1–3.5(–5) mm, base attenuate or cuneate, apex obtuse or acute. Fruiting pedicels divaricate or ascending, straight, slender, 2–5(–6) mm, trichomes stellate, with fewer, simple and forked ones. Flowers: sepals (persistent) oblong, (1.5–)2–3 × 0.7–1.1 mm, pubescent as pedicels; petals (often persistent) white or pale yellow, usually linear to linear-oblanceolate, rarely obovate, 2–3(–4) × 0.3–0.7(–1) mm, apex emarginate, glabrous or sparsely stellate-pubescent abaxially; filaments (slender) not appendaged, toothed, or winged, 1–1.5 mm; anthers ovate, 0.15–0.2 mm. Fruits orbicular, (2–)3–4(–5) mm diam., apex emarginate or truncate; valves uniformly inflated at middle, strongly flattened at margins, sparsely stellate-pubescent; ovules 2 per ovary; style (slender), 0.3–0.6(–1) mm, basally stellate-pubescent or glabrous. Seeds oblong to ovoid, compressed, 1.1–2 × 0.7–1.1 mm, margins narrow, ca. 0.1 mm wide. 2n = 32.
Phenology: Flowering May–Jul.
Habitat: Roadsides, railways, waste grounds, disturbed sites, grassy areas, fields, sagebrush flats, limestone ledges or bluffs
Elevation: 0-1800 m
Introduced; Alta., B.C., Man., Nfld. and Labr. (Nfld.), Ont., Que., Sask., Alaska, Ariz., Calif., Colo., Conn., Idaho, Ill., Ind., Iowa, Kans., Maine, Md., Mass., Mich., Mont., N.J., N.Mex., N.Y., Ohio, Oreg., Pa., R.I., S.Dak., Utah, Vt., Va., Wash., W.Va., Wis., Wyo., Europe, sw Asia, n Africa.