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Glossary

Last Updated: Spring 2012


Synonyms: NONE

Family: Apiaceae

Home Range/U.S. Introduction:
Giant hogweed is native to the Caucasus Mountains and temperate regions of southwestern Asia. It was originally introduced into the United States as a garden ornamental where it has escaped and has become naturalized in some regions.

U.S. Range Map:



USDA, NRCS. 2012. The PLANTS Database (http://plants.usda.gov, 18 June 2012). National Plant Data Team, Greensboro, NC 27401-4901 USA.

Species Description:
Giant hogweed is a biennial or perennial herb that can attain heights of 5-6 meters. The compound leaves with 3 serrated to lobed leaflets may reach 1-1.5 m in width. The hollow stems, 5-10 cm in diameter, are distinctively covered with dark reddish-purple spots and pustulate bristles. The inflorescence is a large broad flat-topped compound umbel up to .75 m containing numerous small white flowers. The fruit is an oval, brown schizocarp with a broadly rounded base and broad marginal ridges containing easily visible resin canals.

Habitat/Growth Characteristics:
Giant hogweed is very similar in appearance to the native cow parsnip (H. maximum) only it is much larger. It is taller, often twice as tall, the leaves are larger, and the inflorescence is much wider. The stems of giant parsnip are reddish purple and covered with coarse hairs while the native parsnip has less coloration on the stem and the hairs are much finer. Giant parsnip plants flower and die after the second season of growth while others continue to flower for several years. Reproduction is by seed or by perennating buds that develop from the root crown. Plants sprout early in the spring from roots or seeds. By late spring plants bolt and flowering begins in mid-May to mid-June and lasts several weeks. By late summer the plants begin to senesce, dying back to the roots however the dried stalk and bare flower stems may persist through fall and winter.

Problems:
Giant hogweed thrives in moist soils and can form monocultures in ravines and riparian areas outcompeting native species. It is also found along roadsides, railroad tracks and other disturbed areas. The plant is a health hazard because it contains furocoumarins that cause severe photo-dermatitis. Exposure to the plants clear watery sap followed by exposure to sunlight produces painful burning blisters that may develop into purplish or blackened scars.