4. Sisymbrium polyceratium Linnaeus, Sp. Pl. 2: 658. 1753.
Chamaeplium polyceratium (Linnaeus) Wallroth
Annuals; (densely leafy through-out); often glabrous. Stems (simple or few to several from base), erect or ascending to subprostrate, branched distally, 1-5(-7) dm, glabrous. Basal leaves (soon withered); initially rosulate; petiole (1-)2-5(-6.5) cm; blade oblanceolate to lanceolate (in outline), 2-7(-10) cm × 10-30(-45) mm, margins sinuate- or runcinate-pinnatifid to coarsely dentate; lobes 3-6 on each side, often triangular, slightly smaller than terminal lobe, margins dentate or subentire. Cauline leaves (sometimes bracts, several), similar to basal, (shortly petiolate); blade margins dentate or subentire, (surfaces glabrous or sparsely puberulent at and near margin). ( Inflorescences 2-4(-6)-fasciculate, or flowers solitary and axillary, bracteate throughout.) Fruiting pedicels ascending to erect, stout, narrower than fruit base, 0.5-1(-2) mm. Flowers: sepals erect, oblong, 1-1.5 × 0.3-0.5 mm; petals spatulate, 1.5-2 × 0.4-0.6 mm, claw 0.6-1 mm; filaments (erect, yellowish), 1.2-1.7 mm; anthers ovate, 0.3-0.5 mm. Fruits (erect to ascending), subulate-linear, recurved, straight, slightly torulose, stout (widest at base), 1-2(-2.3) cm × 0.9-1.7 mm; valves usually glabrous, rarely puberulent; ovules 20-44(-54) per ovary; style 0.5-1 mm; stigma slightly 2-lobed. Seeds 0.7-1 × 0.4-0.5 mm. 2n = 28.
Flowering Mar-Jun. Waste grounds, disturbed sites, roadsides; 0-200 m; introduced; Pa., Tex.; Europe; w, c Asia; nw Africa.