Ambrosia artemisiifolia L.

Erect annual, 30–100 cm tall. Stems moderately clothed in short patent hairs and long erect hairs above, becoming glabrous below, much-branched. Lvs petiolate, moderately to densely clothed in short patent hairs below, less hairy above, often with long marginal hairs at base of petiole, deeply 2–3-pinnatisect, ovate, up to 15 cm long; ultimate segments (1)–2–7 mm wide; upper cauline lvs smaller, ± apetiolate and finally 1-pinnatisect. ♂ capitula pedunculate, 3–5 mm diam.; involucre saucer-shaped, shallowly lobed and usually ciliate. ♀ capitula solitary or clustered. Fruiting involucre glabrous or sparsely hairy, distinctly veined, 3–5 mm long, with a single series of 1–6 short spines around the flattened top; terminal beak 1–1.5 mm long.

[From: Webb et al. (1988) Flora of New Zealand. Volume 4.]

Flowering: Mar.–May.