Giant Hogweed

(This column first appeared in the July 26, 1999 Buffalo News.)

    Joyce French of Marilla called early last week to tell me about a giant plant she found along a rural road. Recognizing it as an unusual species, she stopped to investigate it and unfortunately in the process got some of its sap on her arms. Before she talked with me, Mrs. French called Richard Zander at the Buffalo Museum of Science. He identified the plant as either cow-parsnip or giant hogweed, but he also warned her not to touch it as the giant hogweed is poisonous.

    Too late. When she talked with Dr. Zander, Mrs. French had had no ill effects from her experience, but by the time she called me her arms were deeply burned and blistered. Now the Buffalo Poison Control Center tells her that she must keep her arms covered all summer to avoid further damage.

    Unfamiliar with either of these plants, I obtained directions from Mrs. French and a few evenings later Doris and I drove out to Marilla to look for this specimen. Although her instructions were detailed and easy to follow, we could not find it. We checked the area twice with no luck. It seemed impossible that we had failed to see what was said to be a giant plant.

    As a last resort I stopped at the Creekside Farm home of Jim and Sue Miller who Mrs. French had said might help me. Sure enough, Jim graciously joined us for a drive back to where we had missed the plant and there it was, chopped down and lying on the ground. We hadn’t considered looking underfoot for something ten feet tall.

    Even lying brown and withered, this was clearly a toppled monster, indeed a giant hogweed, Heracleum mantegazzianum. (I include the Latin name because other plants are occasionally called hogweed.)

    Miller then took me into a wooded grove where he showed me more than a dozen more of these plants. Although many of them stooped in grotesque poses, victims of our drought, a few stood upright well over our heads. I felt as though I was in a prehistoric jungle. Not only were the plants huge, but some of their deeply serrated leaves and Queen Anne’s lace-like flower heads measured a yard across.

    Sure enough, my copy of the new Wildflowers of New York in Colorby William K. Chapman and others includes with its description of giant hogweed this comment: "Contact with this plant, which looks like a cow-parsnip, causes painful burning blisters in susceptible people."

    This was clearly worth investigating. Zander and state botanist Richard Mitchell provided references on poisonous plants. It turns out that, unlike nettles that penetrate the skin to release histamines and poison ivy that causes an allergic rash, giant hogweed produces what are called phytophototoxins. That jawbreaker is easily parsed: phyto for plant; photo, light; and toxin, poison. Its chemicals work indirectly, sensitizing the skin to ultraviolet light. Subsequent exposure to the sun or even neon light can produce severe secondary burns with enormous blisters.

    One book on plant poisons* warns, "It is particularly dangerous to children since the hollow stems are well suited for peashooters, popguns and whistles. Blisters and scarring follow around the mouth and eyes."

    A native of the Caucasus Mountains in Russia, giant hogweed was brought to this country to serve as a garden exotic. In upstate New York it has escaped and is now occasionally found as these were along meadow edges, streams and roadsides.

    Because of its danger to those who are allergic and especially to children, botanists suggest destroying giant hogweed wherever it grows wild.

    Given Mrs. French’s experience, I heartily agree. -- Gerry Rising


* James W. Hardin and J. M. Arena, Human Poisoning from Native and Cultivated Plants,2nd edition (Durham, North Carolina: Duke University Press, 1974)

Other recommended books about poisons:

There are also some excellent web resources related to giant hogweed. Among those I found are: