Roman-wormwood

Ambrosia artemisiifolia, common ragweed, is an erect annual herb of the daisy family (Asteraceae) reaching 0.3 to 1.5 m tall. Its much-branched, hairy, often reddish stems bear soft, fern-like leaves that are deeply twice-pinnately divided into narrow lobes, grass-green above and paler beneath, resembling the foliage of mugwort (Artemisia). The plant is monoecious and wind-pollinated: numerous tiny greenish-yellow male flower heads hang in slender terminal spikes, while inconspicuous female heads cluster in the leaf axils below them. The fruit is a small, woody, top-shaped bur bearing several short spines. Native to North America, it is a common weed of disturbed ground, fields, roadsides and waste places, flowering in late summer and autumn. Its copious airborne pollen is a leading cause of hay fever, and the species has become a widespread invasive weed in Europe and elsewhere.