Ambrosia artemisiifolia L.
annual ragweed
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.
N.: Whangarei, Auckland, Wellington; S.: Molesworth, Christchurch.
N. America 1911
Waste places, cultivated land.
FL Mar-May.
Annual ragweed appears superficially similar to Artemisia vulgaris (Anthemideae), but is easily distinguished by the unisexual capitula with a fused involucre, and the lvs which are not aromatic. Ragweed is only known in N.Z. as a casual and seed impurity.
