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RAGWEED
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Ragweed is any of about 35 species of widely distributed, annual or perennial plants of the genus Ambrosia in the daisy family, Compositae. The common ragweed, A. artemisiifolia, is a hairy-stemmed annual growing to about 1.5 m (5 ft) high, with usually deeply divided leaves. Its minute, greenish flowers with yellow stamens are borne in tiny clusters spaced along a slender, erect stalk. The giant ragweed, A. trifida, an annual with three-lobed leaves, reaches a height of 4.5 m (15 ft). Ragweed pollen is the most prevalent cause of autumn hay fever (see ALLERGY) in the United States. The seedlike fruits form an important part of the winter diet of birds.
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