Issue 7, June 6, 2016

Giant Hogweed? Maybe its Cow Parsnip, Poison Hemlock, or Purple Angelica...

This week, we have received a couple of calls regarding the possibility of giant hogweed. Now is the time of year when giant hogweed starts to bloom. As one of our most unwanted invasive species in Illinois, we definitely want to know if there are any populations. But, please remember, giant hogweed can easily be confused with several other plants. These look-a-likes are also being observed across the state at this time.

Giant Hogweed. This plant can grow to heights of 10 to 15 ft and a width of 5 ft. It is a biennial or short lived perennial that has a mostly green hollow stem with reddish purple raised spots along with coarse short hairs on the stalk. The stem can grow to 2 to 4 inches in diameter. The plant has small white flowers in flat umbels that bloom in mid-May through July. The seeds are elliptical shaped and one plant can produce up to 20,000 seeds. After seeding, the plant dies back to the taproot which can live throughout the winter.

In addition to being an invasive weed that can quickly overtake an area by crowding out other plants, giant Hogweed is also harmful to humans by creating a clear watery sap that can cause burning and blistering on the skin when combined with sunlight and can also cause blindness. This sap can get onto someone just by brushing by the leaves or breaking the stem or leaves. It is highly recommended that when dealing with this plant one should wear gloves and protective clothing to allow no contact with skin.

Cow Parsnip, Poison Hemlock, and Angelica all have similar leaves and flowers and may be found in similar habitats. However, all of these plants are dwarfed in size by giant hogweed. 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 whereas Cow Parsnip flowers are only 6 to 12 inches wide.

Giant Hogweed

Cow Parsnip

Poison Hemlock


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've found a population of giant hogweed, please DO NOT TOUCH it! Instead, take some photos, in particular close up of the leaves, flower heads and stem if you can and report the infestation. You can report it to me at or to Chris -, or call your local Department of Agriculture or University of Illinois Extension Service office. (Kelly Estes)

Kelly Estes

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