18. Cardamine hirsuta Linnaeus, Sp. Pl. 2: 655. 1753.
Annuals; sparsely hirsute basally (at least on petiole of basal leaves), often glabrous distally. Rhizomes absent. Stems erect, ascending, or decumbent, unbranched or branched basally and/or distally, (0.3-)1-3.5 (-4.5) dm, (not flexuous). Basal leaves (persistent to anthesis), rosulate, (5-)8-15(-22)-foliolate, (2-)3.5-15(-17) cm, leaflets petiolulate; petiole 0.5-5 cm, (ciliate); lateral leaflet blade oblong, ovate, obovate, or orbicular, smaller than terminal, margins entire, repand, crenate, or 3-lobed; terminal leaflet (petiolule 0.2-1 cm), blade reniform or orbicular, 0.4-2 cm × 6-30 mm, margins entire, repand, dentate, or 3 or 5-lobed. Cauline leaves 1-4(-6), compound as basal, petiolate, [(0.5-)1.2-5.5 (-7) cm, including petiole], leaflets petiolulate; blade base not auriculate; leaflets similar to basal. Racemes ebracteate. Fruiting pedicels erect to ascending, (2-) 3-10(-14) mm. Flowers: sepals oblong, 1.5-2.5 × 0.3-0.7 mm, lateral pair not saccate; petals (sometimes absent) white, spatulate, 2.5-4.5(-5) × 0.5-1.1 mm; (stamens usually 4, lateral pair often absent, rarely 5 or 6); filaments 1.8-3 mm; anthers ovate, 0.3-0.5 mm. Fruits linear, (torulose), (0.9-)1.5-2.5(-2.8) cm × (0.8-)1-1.4 mm, (often appressed to rachis); ovules 14-40 per ovary; style 0.1-0.6(-1) mm. Seeds light brown, oblong or subquadrate, 0.9-1.3(-1.5) × 0.6-0.9 (-1.1) mm, (narrowly margined). 2n = 16.
Flowering Feb-Jul. Roadsides, clearings, disturbed sites, slopes, cedar glades, mixed woods, meadows, fields, waste grounds, damp places, grassy areas; 0-700 m; introduced; B.C., Ont.; Ala., Ark., Calif., Conn., Del., D.C., Fla., Ga., Ill., Ky., La., Md., Mass., Mich., Miss., Mo., N.J., N.Y., N.C., Ohio, Okla., Oreg., Pa., S.C., Tenn., Tex., Utah, Va., Wash., W.Va.; w Eurasia; introduced also in Central America, South America, e Asia (Japan), South Africa, Australia.
Herbarium specimens of Cardamine hirsuta have been misidentified as C. oligosperma.