1. Descurainia pinnata (Walter) Britton (tansy mustard)

Pl. 319 a–c; Map 1341

Stems (10–)20–50(–80) cm long. Leaves 1–10 cm long, with or without stalked glands, the lower leaves 2 times pinnately dissected, the upper ones reduced in size and often 1 time pinnately dissected. Sepals 1–2 mm long. Petals 1.0–3.5 mm long, light yellow, sometimes fading to white upon drying. Fruits club-shaped or oblong, 5–10(–15) mm long, 1–2 mm wide, blunt or rounded at the tip, the valves with 1 midnerve. Styles 0.1–0.2 mm long. Seeds 10–40 per fruit, at least in part in 2 rows in each locule. 2n=14, 28, 42. March–July.

Common throughout Missouri (North America). Banks of streams and rivers, openings of bottomland and mesic upland forests, ledges of calcareous bluffs, glades, and prairies; also fallow fields, railroads, roadsides, and open, disturbed areas.