2. Brassica napus L. (rape, rapeseed, rutabaga, Swedish turnip)

Pl. 315 g–i; Map 1325

Plants annual or biennial, glabrous or nearly so, glaucous, the rootstock sometimes thickened and somewhat fleshy. Stems 30–150 cm long. Basal and lower leaves often absent at flowering, 5–25(–40) cm long, irregularly pinnately divided or lobed into 5–13 irregularly toothed divisions, petiolate but sometimes with rounded auricles at the base, mostly obovate in outline. Stem leaves progressively reduced toward the tip, the uppermost 2–5 cm long, sessile, the bases clasping and with rounded auricles of tissue, linear to narrowly oblanceolate in outline. Flowers not overtopping the buds. Sepals (5–)6–10 mm long. Petals (0.9–)1.0–1.6(–1.8) mm long, usually pale yellow. Fruits (3.5–)5.0–9.5(–11.0) mm long, ascending or spreading, circular in cross-section or nearly so, the slender, tapered beak and style (5–)9–15 mm long. Seeds 24–40(–60) per fruit, globose, (1.2–)1.5–2.5(–3.0) mm in diameter. 2n=38. April–September.

Introduced, uncommon in northwestern and eastern Missouri (not known from native populations, but presumed to have originated in Europe; widely cultivated and sporadically escaped in North America). Roadsides, disturbed ground.

Brassica napus originated from past hybridization between B. oleracea (2n=18) and B. rapa (2n=20). It can be difficult to distinguish from the latter parent (see key). Some botanists separate this species into two varieties, based upon differences in the rootstocks. In var. napus, popularly known as rape or rapeseed, the rootstock is an unthickened taproot, whereas in var. napobrassica (L.) Peterm., the rutabaga, the rootstock is thickened and somewhat succulent. When plants become established outside cultivation, these differences tend to disappear.

This species is presently very uncommon as an escape from cultivation, but it is expected to become more common as commercial production of rapeseed increases in the state. The specimen from railroads in St. Louis reported by Steyermark (1963) as the original voucher for this species was a misdetermined collection of B. rapa.

Rapeseed is the source of canola oil, which has become very popular as a cooking oil in recent years, as well as having pharmaceutical, chemical, and industrial uses. Increasingly, it is being grown as an alternative crop regionally by farmers in the United States and Canada.