Common ragweed (annual ragweed)
Ambrosia artemisiifolia

Annual, shallow-rooted herb to 2 m high.

Leaves lanceolate to ovate, 1–16 cm long, 1–5 cm wide, bipinnately divided, lobes lanceolate to oblong; alternate at base and sometimes opposite above, green to grey-green, finely hairy to ± glabrous.

Male heads yellow-green; female heads few in clusters, with 1 floret. Bracts forming the fruit c. 3 mm long, with a single row of 4–6 spines or teeth, sometimes less or inconspicuous, and a central beak.