North America contains only 10 species of invasive plants that are toxic. Among them are oleander, manchineel, and deadly nightshade. One of the most attractive of these is the giant hogweed.
The formal name of giant hogweed is heracleum mantegazzianum, although it is sometimes called cartwheel-flower, giant cow parsnip, hogsbane or giant cow parsley. It is in the family Apiaceae. Hogweed grows on other continents, as well, and in New Zealand, it is sometimes called wild parsnip, or wild rhubarb.
It was originally indigenous to the Caucasus region and Central Asia. In the 19th century it was taken to Britain as an ornamental plant. Eventually, it spread to other areas of Europe and beyond, and of course to Canada and the United States.
Hogweed features showy white flowers that arch above a long stem. Situated in a field, the flowers almost beg you to pick them and take them home, perhaps even put a blossom behind your ear.
Don’t do it!
The problem is the toxic sap that fills the stem, the leaves, roots, flowers and seeds of the plant. It causes phytophotodermatitis in human beings. Merely touching the giant hogweed plant can result in enormous, foul smelling blisters that quickly spread all over your body, leaving permanent scars. If your eyes come in contact with the plant, it can even cause blindness.
Giant hogweed has thick leaves that stretch up to five feet, and the plant itself can reach 14 feet in height. The large clusters of white flowers form an umbrella-like pattern, and they are suspended atop long stems. The stems themselves are green in color, with fine white hairs.
If you think you may have had contact with hogweed, wash the affected area with soap and cold water at once. Stay out of the sun for 48 hours, and see a doctor as soon as possible. The recommended treatment is topical steroids. If they are applied quickly, they can often reduce the severity of the reaction.