ragweed

Any of various weeds of the genus Ambrosia of the composite family, having small, greenish, unisexual flower heads and producing abundant pollen that is one of the chief causes of hay fever.

Ragwort.

Any plant of the composite genus Ambrosia; especially, the common North American species A. trifida, the great ragweed or horse-cane, and A. artemisiæfolia, the Roman wormwood or hogweed.

The ragwort or St.-James-wort, Senecio Jacobæa.

A common American composite weed (Ambrosia artemisiæfolia) with finely divided leaves; hogweed.

a coarse American herb (Ambrosia trifida), with rough three-lobed opposite leaves.

A plant of the genus Ambrosia. These weeds are particularly noted for producing pollen which people with hay fever are allergic to.

any of numerous chiefly North American weedy plants constituting the genus Ambrosia that produce highly allergenic pollen responsible for much hay fever and asthma

widespread European weed having yellow daisylike flowers; sometimes an obnoxious weed and toxic to cattle if consumed in quantity