|ragweed (Ambrosia spp.)||
ragweed (Ambrosia spp.; COMPOSITE FAMILY [Asteraceae]) Annual or perennial herbs of variable size with racemes of inconspicuous, green, wind-pollinated flowers. Leaves deeply lobed or divided into narrow segments. Opportunistic weeds whose copious pollen is a principal cause of hay fever. Flowers in late summer and fall. 
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