1. Brassica juncea (L.) Czern. (brown mustard, leaf mustard, Chinese mustard, Indian mustard)

Pl. 314 a–c, 315 a–c; Map 1324

Plants annual, glabrous or nearly so, glaucous. Stems (20–)30–100(–180) cm long. Basal and lower leaves (4–)10–30(–80) cm long, pinnately divided into 5–9 irregularly toothed divisions, petiolate, elliptic to obovate in outline. Stem leaves progressively reduced toward the tip, the uppermost 2–5(–10) cm long, short-petiolate or sessile with nonclasping bases, oblanceolate to elliptic or nearly linear in outline. Flowers usually not overtopping the buds. Sepals 4–8 mm long. Petals 7–13 mm long, pale yellow. Fruits (20–)30–50(–60) mm long, spreading to ascending, not appressed to the inflorescence axis, circular in cross-section or nearly so, the beak and style (4–)5–10 mm long. Seeds 12–30(–40) per fruit, globose, 1.0–1.7 mm in diameter. 2n=36. April–September.

Introduced, widely scattered in Missouri (native of Europe, Asia, widely naturalized in the New World). Pastures, margins of crop fields, roadsides, railroads, and open, disturbed areas.

This species is occasionally cultivated as a leafy, green vegetable. In Asia, the seeds are sometimes used as a spice. They are also occasionally used in the preparation of massage oils. It is thought to have originated in Asia through past hybridization between B. nigra and B. rapa (Al-Shehbaz, 1985). Numerous leafy forms are cultivated in China and cooked as a green vegetable.

A related species that should be searched for in Missouri is B. tournefortii Gouan, an aggressive weed that was first reported as naturalized in the southwestern United States and that has spread at least as far east as Texas within the past few decades (Rollins, 1993). It will probably arrive in the state at some point either along railroad tracks or roadsides. This species differs from B. juncea in having hairy rather than glabrous lower leaves and stem bases, more persistent rosettes of basal leaves with more numerous divisions (15–30), and shorter petals (4–6 mm).