Eastern Forest Threat Center - Giant Hogweed

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Giant hogweed plants

Giant hogweed plants

USDA APHIS PPQ Archives, Bugwood.org

Giant Hogweed
Heracleum mantegazzianum

Giant hogweed is native to Europe. It was originally introduced into the U.S. as an ornamental or spice.

Keywords: Apiaceae, biennial, perennial, herb, hollow stems and stalks, bristles, broad flower umbel, toxic sap, noxious weed; Common names: cartwheel flower

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Threat Description

Giant hogweed is a biennial or perennial herb in the carrot family that grows 15 to 20 ft. in height with stout dark reddish-purple stems and spotted leaf stalks, both hollow with sturdy bristles, and compound leaves with three leaflets expanding up to 5 ft. in breadth. The inflorescence, up to 2 ½ ft. in diameter, is a broad flat-topped umbel composed of small white florets that produce large elliptic dry fruits. After flowering, it produces up to 1500 large flattened elliptic dry seeds per flower head. It is common along railroads, roadsides, rights-of-way, vacant lots, streams, rivers, uncultivated or waste lands, and agricultural areas. Because of its size and rapid growth, giant hogweed aggressively out-competes native plant species, reducing the amount of suitable wildlife habitat. It dies back during winter, leaving bare ground that can lead to increased soil erosion. Giant hogweed also poses a public health hazard. It contains a substance within its sap that makes skin sensitive to ultra violet light, resulting in severe burns to affected areas. Swelling and severe, large, painful, watery blisters usually appear 15 to 20 hours after contact with the sap and sunlight.