Thlaspi arvense
Sp. Pl. 2: 646. 1753.
Plants (sometimes glaucous), glabrous throughout. Stems (0.9–)1.5–5.5(–8) dm. Basal leaves not rosulate; petiole 0.5–3 cm; blade oblanceolate, spatulate, or obovate, 1–5 cm × 4–23 mm, base attenuate or cuneate, margins entire, repand, or coarsely dentate, apex rounded. Cauline leaves: blade oblong, (0.5–)1.5–4(–8) cm × (2–)5–15(–25) mm, apex rounded, obtuse, or subacute. Fruiting pedicels straight or slightly upcurved, (5–)9–13(–15) mm. Flowers: sepals (1.5–)2–3(–3.3) × 1–1.5 mm; petals (2.4–)3–4.5(–5) × (0.8–)1.1–1.7 mm, narrowed to clawlike base (ca. 1 mm), apex obtuse or emarginate; filaments (1–)1.5–2.2 mm; anthers 0.3–0.5 mm. Fruits obovate or suborbicular, (0.6–)0.9–2 cm × (5–)7–20 mm, base obtuse or rounded, apex deeply emarginate, notch ca. 5 mm deep; wings broad throughout, 1–1.5 mm wide basally, 3.5–5 mm wide apically; ovules 6–16 per ovary; style 0.1–0.3 mm. Seeds (1.2–)1.6–2(–2.3) × 1.1–1.3 mm, concentrically striate. 2n = 14.
Phenology: Flowering Mar–Aug.
Habitat: Roadsides, fields, waste places, lawns, gardens, railroad tracks, stream banks, bluffs, thickets, slopes, floodplains, woods
Elevation: 0-2000 m
Distribution
Introduced; Alta., B.C., Man., N.B., Nfld. and Labr., N.W.T., N.S., Ont., P.E.I., Que., Sask., Yukon, Ala., Alaska, Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo., Europe, Asia.
Discussion
Thlaspi arvense is a cosmopolitan weed of Eurasian origin. Cattle feeding on it develop tainted milk.