Giant Hogweed Or Cow Parsnip?

By Jaqi Christopher, DNR Forest Invasive Plant Specialist, Rhinelander, Jacquelyn.christopher@wisconsin.gov

Giant hogweed is a large invasive species commonly confused with the native look-alike cow parsnip. Although giant hogweed is uncommon in Wisconsin, it’s important to know the difference between the two.

Person standing with giant hogweed towering over them.

Giant hogweed can invade woodlots and get 8-20 feet tall. Photo Credit: Ramona Shackleford

Firstly, giant hogweed is a huge plant. It can grow 8-20 feet tall with a purple blotched stem 2-4 inches in diameter with coarse hairs. The white umbrella-shaped flower clusters can be up to 2.5 feet wide, and the leaves can be up to 5 feet wide. This plant is more like the size of your patio umbrella than any native flowers!

Giant hogweed is a concern due to its sap that can cause phytophotodermatitis, an adverse reaction on the skin. However, this harsh skin irritation only occurs when the plant is broken open to expose sap.

While both giant hogweed and cow parsnip may cause skin irritation, cow parsnip is much less harmful. This native, pollinator-friendly plant is often mistaken for giant hogweed but is much smaller than its invasive counterpart. Cow parsnip can grow 5-8 feet tall with white flower clusters only about a foot wide. The stems are mostly green with fine white hairs and are 1-2 inches in diameter. The leaves can get up to 2.5 feet wide, about half the size of giant hogweed.

If you think you have found giant hogweed, please email photos that include a size reference, location details and a description of the plant to Invasive.Species@wisconsin.gov.

A cow parsnip with a mostly green stem.

Cow parsnip green stem with fine hairs. Photo: Wisconsin DNR

A giant hogweed stem that is green with purple blotches.

Giant hogweed stem with purple blotches. Photo: Bugwood.org, Rob Routledg, Sault College

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