8. Lepidium perfoliatum L. (shield cress, perfoliate pepper grass)

Pl. 323 a, b; Map 1367

Plants annual or biennial. Stems (7–)10–40(–65) cm long, erect, usually unbranched below the inflorescence, usually sparsely pubescent with short, spreading hairs toward the base, glabrous and glaucous toward the tip. Leaves of 2 types, the basal and often lower stem leaves (2–)4–13(–19) cm long, 2 or 3 times pinnately divided with linear divisions, minutely hairy, the median and upper stem leaves 0.7–3.0(–4.0) cm long, ovate to circular, the bases perfoliate or strongly clasping the stems with rounded, strongly overlapping auricles, the margins entire to minutely toothed, glabrous and glaucous. Sepals 0.8–1.0(–1.3) mm long, broadly elliptic. Petals 1.0–1.5(–1.9) mm long, yellow. Stamens 6. Styles 0.1–0.3 mm long. Fruits 3.0–4.0(–4.8) mm long, ovate to nearly circular in outline, flattened, the tip with a minute notch and short, narrow wings. Seeds 1.6–2.0(–2.3) mm long, elliptic in outline, narrowly winged all around, the surface with a fine, netlike or honeycomb-like pattern of ridges and pits, reddish or dark brown. 2n=16. April–June.

Introduced, widely scattered in Missouri (native of Europe and Asia, widely naturalized in the western U.S. and adjacent Canada east to Ohio). Railroads and less commonly roadsides and open, disturbed areas.