Issue 8, June 11, 2010

Friend or Foe: Giant Hogweed and Its Look-alikes

Giant Hogweed (Heracleum mantegazzianum) is a member of the carrot or parsnip family (Apiaceae). While many members of this family are native to Illinois, Giant hogweed is an invasive species that was brought from Asia in the 1900's. This plant was most likely brought as an ornamental because of its showy white flowers and impressive size. However, it is very aggressive and noxious. When bare skin comes into contact with this plant, a hazardous sap is deposited that when exposed to sunlight causes severe skin irritation such as burning blisters. The resulting scars may last for several years. For these reasons, this plant is not only of ecological concern, but it is a public health hazard.

Like many members of the carrot family, this plant has lacy white flowers and wide fern like leaves. Giant Hogweed is generally easy to distinguish because of its large size. Plants in Illinois that have a similar appearance to Giant Hogweed include; Water Parsnip, Cow Parsnip, Queen Anne's Lace, Water Hemlock, Poison Hemlock, and Angelica. While these plants have similar leaves and flowers, all are dwarfed by Giant Hogweed which grows 10-15 feet tall. The only 'look-alike' that comes close in size is the Cow Parsnip at 4-9 feet tall. Other important differences between these two plants include the leaves which are 5 feet wide on the Giant Hogweed and only 1 foot wide on the Cow Parsnip. In addition, the Hogweed flowers are 2.5 feet wide where as Cow Parsnip flowers are only 6 to 12 inches wide.

Left: Man standing next to a fully grown Giant Hogweed plant (image courtesy of the USDA). Right: Pen on a Giant Hogweed blossom (image courtesy of

Due to the noxious nature of the plant, ALWAYS wear skin protection when coming into contact with Giant Hogweed. Giant hogweed is still rare in Illinois. While visitors in natural areas are unlikely to encounter this plant, it never hurts to keep a watchful eye for this and other invasive plants. If you think you may have Giant Hogweed on your property or you want more information feel free to contact Illinois Cooperative Agricultural Pest Survey (CAPS).--Irenka Carney and Stephanie McLaughlin, research assistants with the Illinois CAPS program

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