Burr ragweed

Erect perennial up to 2 m high and forming large colonies.

Leaves alternate, ± ovate to lanceolate, c. 16 cm long, 10–15 cm wide, bipinnately divided, lobes linear to lanceolate, green to grey-green, finely hairy.

Heads yellow-green; female heads 4 mm diam., abundant in massive clusters, each with 1 or rarely 2 florets. Bracts forming the fruit c. 4 mm long, covered with short hooked spines.