Annuals or biennials; (taproot slender or swollen); (glaucous), glabrous, glabrescent, or pubes-cent, (trichomes coarse). Stems branched distally, 3-13 dm. Basal leaves (rosulate when biennial); petiole (often winged), to 15 cm; blade lyrate-pinnatifid, ± pinnately lobed, 5-25(-40) cm × 20-70(-100) mm, lobes 0-6 each side, (smaller than terminal), surfaces (glaucous), glabrous or sparsely hairy when immature, glabrescent, or, rarely, pubescent. Cauline leaves (middle and distal) sessile; blade base auriculate or amplexicaul, (margins entire). Racemes not paniculately branched, (buds overtopping or equal to open flowers). Fruiting pedicels spreading to ascending (slender), 1-3 cm. Flowers: sepals (5-)6-10 × 1.5-2.5 mm; petals golden or creamy to pale yellow, broadly obovate, 10-16 × (5-)6-9(-10) mm, claw 5-9 mm, apex rounded; filaments (5-)7-10 mm; anthers 1.5-2.5 mm. Fruits spreading to ascending, smooth or slightly torulose, terete, (3.5-)5-10(-11) cm × (2.5-)3.5-5 mm; valvular segment with 12-20(-30) seeds per locule, (3-)4-8.5(-9.5) cm, terminal segment usually seedless, rarely 1 or 2-seeded (attenuate-conic, thin), (5-)9-16 mm. Seeds dark brown to black, light brown, or reddish, 1.8-2.7(-3) mm diam.; seed coat finely reticulate-alveolate, not mucilaginous when wetted. 2n = 38.
Brassica napus is both a crop and a sporadically occurring naturalized weed in North America, grown in two forms recognized by some as subspecies. Subspecies napus (rape, rapeseed, or canola) is an annual with slender roots widely cultivated as an oil crop and is the most commonly naturalized. Subspecies rapifera Metzger [= subsp. napobrassica (Linnaeus) Hanelt] (rutabaga, swede, or Swedish turnip) is a biennial with fleshy roots that rarely escapes from cultivation.
Although Brassica napus has been reported as a weed from most southeastern states, it is very likely that most reports represent misidentifications of B. rapa (I. A. Al-Shehbaz 1985). It is difficult to distinguish between plants of B. napus and B. rapa that lack flowers and proximal leaves.
Brassica napus is an allotetraploid derived from hybridization between the B. oleracea complex (n = 9) and B. rapa (n = 10). Its center of origin is uncertain but likely Mediterranean Europe, with molecular data supporting evidence of multiple independent origins between the parental taxa B. oleracea and B. rapa and its related n = 9 species (Song K. et al. 1993). Specimens from West Virginia have not been observed.
Annual herb to 0.8 m tall Stem: upright, bluish green, with a waxy coating (glaucous). Flowers: in branched clusters, pale yellow or cream colored, to 1.8 cm long. Petals four. Stamens six. Fruit: a narrow pod, ascending, 3 - 5 cm long, roundish in cross-section, with a beak. Lower leaves: alternate, pinnately divided, stalkless, to 15 cm long, base lobed, toothed, with a waxy coating (glaucous), sometimes sparsely hairy. Upper leaves: alternate, stalkless, clasping, to 9 cm long, to 3 cm wide, lance-shaped to linear, base lobed, mostly non-toothed, with a waxy coating (glaucous), sometimes sparsely hairy.
Similar species: Brassica napus and B. rapa are the only two Brassica species in the Chicago Region with at least the middle and upper leaves clasping. Brassica rapa is otherwise similar, but it is covered with a waxy coating (glaucous).
Flowering: late April to late May
Habitat and ecology: Introduced from Europe. Grown as a garden vegetable and occasionally escaping but not persisting. Has been found growing spontaneously in a compost pile, along the disturbed area of a railroad, in a grain stubble field, and near a fence at the edge of a wheat field.
Occurence in the Chicago region: non-native
Etymology: Brassica is the Latin word for cabbage.