Cyclachaena xanthiifolia

Cyclachaena xanthiifolia, also treated as Iva xanthiifolia and commonly called giant sumpweed or marsh-elder, is a tall coarse annual herb in the Asteraceae family, native to central North America and now widely naturalised as a weedy invader across Europe and parts of Asia. It typically grows 1 to 3 metres tall with a stout, erect, freely branching stem that is somewhat ridged and finely hairy. The leaves are opposite at least below, long-petiolate, broadly ovate, 10 to 25 cm long, with three to five coarsely serrate or palmately lobed sections, superficially resembling those of common cocklebur (Xanthium). The upper surface is rough-hairy and the lower surface paler and more densely pubescent. The inflorescence is a large, leafy, terminal panicle of small, drooping, greenish flower heads; each head is unisexual or bisexual with inconspicuous disk florets and lacks ray florets. Flowering occurs from late summer into autumn. The pollen is a notable cause of seasonal hay fever. Fruits are small, dark, glabrous achenes lacking a pappus.