Giant Blindness-Causing Weed Is Spreading

Hogweed can be 20 feet tall and appears set to conquer ecosystems across North America. Oh, and it can blind you.

State environmental authorities in Wisconsin are the latest to warn of the dangers of a giant invasive plant whose toxic sap can cause temporary blindness and severe burns and blisters in people unlucky enough to come in contact with it.

But they're not the only ones worried about giant hogweed (scientific name Heracleum mantegazzianum), a plant from central Asia that misguided horticulturists imported to New York state back in 1917, possibly because of the beauty of its umbrella-shaped white flowers. Since then, it's spread across the United States from Maine to Washington state, and across Canada as well.

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In some ways, hogweed is the ultimate nightmare of invasive plants. It can grow to between 8 and 20 feet tall and is hardy enough to survive in everything from below zero to 95-degree temperatures, and could dominate ecosystems across North America.

Hogweed's size enables it to spew thousands of seeds into the wind, and it's capable of expanding its range by as much as a square mile each year, according to a U.S. Forest Service dossier on the plant.

But what really makes hogweed scary is its sap, which contains toxins called furanocoumarins. Those chemicals, once exposed to ultraviolet light from the sun, bind to the DNA in the nuclei of skin cells, causing them to self-destruct.

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That's why if you come across a hogweed plant, be sure not to touch it -- and if you do, wash your skin with soap and cold water as soon as possible, and stay out of the sun for at least 48 hours, according to this list of safety measures from the New York state Department of Environmental Conservation.

The plant has been spreading in Europe and the U.K. as well. Here's a recent news report about a British teenager who got a severe burn on his leg after coming into contact with hogweed.

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