Above: Image © Fritz Geller-Grimm, Wikimedia Commons

Giant hogweed, or Heracleum mentagazzianum, has become a newsworthy invasive species in Canada. Suddenly, it seems to be cropping up everywhere!

But unlike invasive species such as the zebra mussel, this one can strike out at humans directly.

Why the frenzy of fear? The sap of the giant hogweed can cause severe burns and even temporary blindness. It’s a very obnoxious noxious weed!

Did you know?The name Heracleum mentagazzianum is derived from the mythological Hercules and the 19th century Italian neurologist, physiologist, and anthropologist Paolo Mantegazza.

Chemicals called furanocoumarinscause the burns and blindness when activated by UV light. This activation results in phytophotodermatitis, which is just a big word for plant (phyto) and light (photo)-induced inflammation of the skin (dermatitis). When giant hogweed sap gets on your skin, it gets red and itchy and may begin to blister within 48 hours. If the burn is not treated early, it can result in black and purplish scars that can stick around for years. Not pretty. Doctors say the best thing to do if the sap gets on you is to get out of the sun, wash your skin with soap and water, and seek medical attention if your skin gets red and itchy.

Did you know? Furanocoumarins are not all bad. They have long been used to treat psoriasis and other skin conditions.

The best way to prevent getting burned by this weed is to avoid it. It’s hard to miss since giant hogweed can reach two to five metres in height! The plant’s sharply toothed leaves and prickly, purple-spotted stems also distinguish it. Generally, the weed is found in sunny, damp areas, like roadsides, open fields and by streams.

Did you know? Giant hogweed is a major problem in England. The rock band Genesis even wrote a song called “The Return of the Giant Hogweed”.

Hogweed hysteria has hit Canada this summer, but experts generally agree it isn’t necessary to live in fear. The key is to watch where you’re walking (and look up, way up!), the same way you would to avoid poison ivy.

Learn More!







Ecology and Management of Giant Hogweed (Heracleum mantegazzianum). P. Pysek, M.J.W. Cock, W. Nentwig, and H.P. Ravn, ed. 2007. CAB International, Cambridge, Mass., U.S.A

Article first published on September 15, 2010.

Candace Webb

I graduated from the University of Ottawa in 2006 with a PhD in Biology. I am now a postdoctoral fellow at UCLA, studying the funky circadian rhythms of plants. Besides science, I love to write, hike, paint, bike ride, and hang out at the beach.

Une diplômée de l’Université d’Ottawa, j’ai reçu mon doctorat en biologie en 2006. Je suis présentement boursière postdoctorale à l’Université de Californie à Los Angeles, où j’étudie les rythmes circadiens des plantes. En plus des sciences, j’aime écrire, passer du temps à la plage et faire de la peinture, de la randonnée et du vélo.

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