Strongly aromatic annual herb 1–2 m high; stems mostly unbranched, glabrous.
Leaves mostly opposite, pinnate, to 10 cm long; leaflets 3–9, narrow-elliptic to lanceolate, acute, 2–8 cm long, 2–9 mm wide, occasionally wider, finely toothed, glabrous, gland-dotted.
Heads borne in dense terminal panicles; heads 2–5 mm diam.; involucral bracts 3 or 4, almost completely fused into a tube to c. 10 mm long, smooth, glabrous, yellow-green, marked with interrupted streaks. Ray florets 2–4; ligules obovate, 1–3 mm long, yellow. Disc florets 4 or 5, greenish.