Erect annual or biennial, with foetid odour when crushed. Stems hollow, striate, up to 2-(3) m high, usually light green and purple spotted or blotched, sometimes tinged purplish or pink, particularly toward base. Lvs 2-4-pinnate; ultimate segments narrowly or broadly ovate to deltoid, pinnatisect or serrate, 5-40 mm long; petioles light green and purple blotched when mature; stem lvs similar to basal, but shortly petiolate and 1-3-pinnate. Umbels 1-8 cm diam.; rays 4-16; bracts c. 4-8, narrow-triangular, acuminate, reflexed; bracteoles 3-6, triangular, confined to outer side of umbellets. Fls numerous, white, c. 2 mm diam. Fr. dark brown, 2.5-3 mm long; ribs slender, light brown, often crenulate.