5. Arabidopsis halleri (Linnaeus) O’Kane & Al-Shehbaz, Novon 7: 325. 1997.
Herbs, perennial, stoloniferous. Stems (7–)20–65(–80) cm, decumbent, few from base, simple or branched above, basally with simple and 2- or 3-rayed forked trichomes, apically glabrous. Basal leaves rosulate; petiole (5–)1–2.5(–5) cm; leaf blade orbicular to broadly ovate, (1–)2–4.5(–9) x (0.5–)1–1.5(–2.5) cm, adaxially with a mixture of simple and stalked, 1- or 2-forked trichomes, margin pinnatifid to lyrate-pinnatifid and with (1 or)2–4(–7) suborbicular lateral lobes on each side; terminal lobe suborbicular, much larger than lateral ones, sometimes coarsely dentate, rarely entire or repand, apex obtuse; cauline leaves shortly petiolate, (3–)5–20(–24); blade of middle and lower ones ovate to oblong or lanceolate, (0.5–)1–2.5(–8) x (0.2–)0.5–1.5(–3) cm, coarsely toothed or rarely lobed, gradually reduced in size upward. Fruiting pedicels divaricate or slightly reflexed, straight, (0.5–)0.8–1.3(–2) cm. Sepals 1.5–3(–3.5) mm, glabrous or apically with few simple trichomes, lateral pair saccate; petals white, lilac, or purplish, obovate, 4–7(–8) x 2–3.5(–4) mm; claw entire; filaments white, 2–2.5 mm; ovules 14–18 per ovary. Fruits linear, flattened, torulose, (0.9–)1–2.5(–3) cm x 0.6–1 mm; replum constricted between seeds; valves not veined or with an obscure midvein; gynophore slender, to 0.7 mm; style slender, to 1 mm. Seeds oblong, flattened, light brown, 0.8–1.2 mm, wingless; cotyledons accumbent. 2n=16.
Flowering: May–Aug.
Habitats: slopes, forest margins, rocky crevices, gravelly or grassy slopes, forests, shaded and most areas.
Elevation: 0–2600 m.
Distribution: Albania, Austria, Belgium, Bosnia and Herzegovenia, Croatia, Czech Republic, N France, Germany, N and C Italy, Moldova, Poland, Romania, Serbia, Slovakia, Slovenia, Switzerland, and S Ukraine; NE China, Korea, Japan, Russian Far East, Taiwan.
Three subspecies.