3. Brassica nigra (L.) W.D.J. Koch (black mustard)

Pl. 315 d–f; map 1326

Plants annual, sparsely to densely pubescent, at least near the base, often somewhat glaucous above. Stems 30–200(–310) cm long. Basal and lower leaves 6–25(–40) cm long, irregularly pinnately divided or lobed into 3–7 irregularly toothed divisions, sometimes unlobed, petiolate, elliptic to obovate in outline. Stem leaves progressively reduced toward the tip, the uppermost 1–5 cm long, petiolate with nonclasping bases, oblanceolate to elliptic in outline. Flowers usually not overtopping the buds. Sepals (3–)4–6(–7) mm long. Petals (5–)7–11(–13) mm long, usually bright yellow. Fruits (5–)10–25(–27) mm long, erect, appressed to the inflorescence axis, somewhat 4-angled in cross-section, abruptly narrowed to a linear beak and style (1–)2–5(–6) mm long. Seeds 4–10(–16) per fruit, globose, 1.2–2.0 mm in diameter. 2n=16. April–November.

Introduced, widely scattered in Missouri, mostly north of the Missouri River (native of Europe, Asia, widely naturalized in North America). Pastures, margins of crop fields, roadsides, railroads, and open, disturbed areas.

Until recently replaced by B. juncea, B. nigra was the chief source of seed used in making table mustard, which also contains extracts from the seeds of white mustard, Sinapis alba. Extracts from the seeds are also used medicinally and in the preparation of some scented soaps.