2. Lepidium campestre (L.) R. Br. (field cress, cow cress, field pepper grass)

Thlaspi campestre L.

Pl. 323 c, d; Map 1361

Plants annual. Stems (8–)12–50(–60) cm long, erect, usually unbranched below the inflorescence, densely pubescent with short, spreading hairs. Leaves (1–)2–7(–8) cm long, sessile, clasping the stem with pointed auricles, the blades narrowly oblong to oblanceolate in outline, the margins entire to shallowly toothed (the basal leaves less commonly 1 time pinnately lobed), densely short-hairy. Sepals (1.0–)1.3–1.8 mm long, narrowly elliptic. Petals (1.5–)1.8–2.5(–3.0) mm long, white. Stamens 6. Styles 0.1–0.5 mm long. Fruits (4–)5–6 mm long, ovate to broadly oblong in outline, the tip shallowly notched and relatively broadly winged, flattened, the valves with minute papillae. Seeds 2.0–2.3(–2.8) mm long, obovate in outline, not winged, the surface minutely papillate, reddish gray to dark brown or black. 2n=16. April–June.

Introduced, scattered nearly throughout Missouri (native of Europe and Asia, widely naturalized in the U.S. and Canada). Roadsides, railroads, fallow fields, pastures, and open, disturbed areas.

Superficially, this species resembles the species of Thlaspi found in Missouri. However, in addition to having only 1 seed per locule (vs. 3–8), L. campestre is densely hairy, whereas species of Thlaspi are glabrous.