6. Cardamine hirsuta L. (hoary bitter cress)

Pl. 317 f; Map 1336

Plants annual. Stems (3–)10–35(–45) cm long, glabrous or with sparse, spreading hairs near the base. Basal leaves numerous at flowering time, (1.5–)3.0–10.0(–13.0) cm long, short-petiolate, the petioles with spreading hairs, pinnately compound with 3–15(–23) glabrous leaflets, the lateral leaflets circular to ovate or obovate, entire or with 1–3 irregular teeth, tapered to a sessile or short-stalked base, this not expanded along the rachis, the terminal leaflet usually broader than the lateral ones. Stem leaves 2–5(6), 1–5(–7) cm long, pinnately compound with 5–15(–21) leaflets, these linear to oblanceolate or oblong to ovate, sometimes hairy on the upper surface. Sepals 1.0–2.5 mm long, green. Petals 1.5–4.0(–5.0) mm long, white. Stamens 4(6). Styles 0.1–0.6(–1.0) mm long. Fruits (9–)15–25(–28) mm long. Seeds 0.9–1.3(–1.5) mm long, oval to oblong in outline, the surface with a fine, netlike or honeycomb-like pattern of ridges and pits, orange. 2n=16. March–April.

Introduced, uncommon and widely scattered in Missouri (native of Europe, Asia, naturalized nearly worldwide). Sandy banks of streams and moist depressions of sandstone glades; also lawns and pastures.

This uncommon weed sometimes is confused with C. pensylvanica and C. parviflora, but it may be distinguished by characters in the key to species above. For a discussion of differences between this complex and Planodes virginica, see the treatment of that species.