Giant hogweed is designated as a Federal Noxious Weed, because it produces sap that causes skin sensitivity to UV radiation and leads to blistering and severe burns.
Giant hogweed is a herbaceous biennial that can grow up to 7-20 feet tall. Hollow stems are 2-4 inches in diameter with dark reddish-purple spots and bristles.
The leaves are deeply lobed, sharply pointed. They can be up to 9.8 feet in breadth.
Flowering occurs in late spring to early summer. The white flowers are on a large umbrella-shaped head at that can be up to 2.5 feet in diameter, with 50+ rays per cluster.
Flattened, 3/8 inch long oval dry fruits that have a broadly rounded base and broad marginal ridges.
Because of its size and rapid growth, giant hogweed is an aggressive competitor capable of displacing native plants. It dies back during the winter months, leaving bare ground open to erosion on riverbanks and steep slopes. The sap of giant hogweed makes human skin sensitive to ultraviolet light, resulting in severe burns and blisters. Contact with the eyes can cause permanent blindness.
Giant hogweed is native to Europe and Asia. It was first introduced into the United States in 1917 for ornamental purposes.
Giant hogweed can invade a variety of habitats but prefers moist, disturbed soils such as riverbanks, ditches and railroad right-of-ways.
Giant hogweed sprouts in early spring and flowers early July. This perennial plant dies back after flowering, leaving tall dead stalks. It forms perenating buds which lie dormant through winter until the next growing season. It reproduces by seed dispersal only, not vegetatively. Each flower head contains approximately 1500 seeds, which can remain viable for up to ten years.
Terry English, USDA APHIS PPQ, Bugwood.org
Donna R. Ellis, University of Connecticut, Bugwood.org
Rob Routledge, Sault College, Bugwood.org
Robert Videki, Doronicum KFT, Bugwood.org
USDA Aphis PPQ Oxford NC, Bugwood.org
Vermont Chapter of The Nature Conservancy