Height: 15–40 cm (6–16 in.). Stem abundantly hairy.
Flower: Corolla regular (actinomorphic), pale yellow, approx. 0.5 cm (0.2 in.) across; petals four, 3.5–4.5 mm (0.14–0.18 in.) long. Sepals 4. Stamens 6, of which 2 short and 4 long. Gynoecium fused, a single carpel. Inflorescence an elongating raceme in fruiting stage.
Leaves: Alternate, lower leaves stalked, stem leaves stalkless, amplexicaul. Blade with sagittate base.
Fruit: Many-seeded, pear-shaped (pyriform), slightly oval, already hard-shelled when young, 4–6 mm (0.16–0.24 in.) long silicula, terminated by an approx. 2–3 mm (0.08–0.12 in.) long bristle. Stalk ascending oblique.
Habitat: Railways, mills, harbours, rubbish tips, wasteland, sometimes lawns.