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Resources |  Invasive Species
Giant Hogweed (Heracleum mantegazzianum)


Giant hogweed was introduced from Europe, presumably as an ornamental, and has escaped along roadsides, streambanks and waste areas in scattered localities in southern Ontario.  It is now being seen in the Lake Huron coastal area. It is distinguished by its huge size, its very large, compound leaf blades, its tall, thick, hollow, often sharply roughened stems, and its large flat-topped compound inflorescence with white flowers and large, flat fruits with prominent dark-coloured oil tubes. Flowering inflorescences are often heavily infested by aphids.

Often Mistaken For


Giant hogweed has been mistaken for other species, especially others in the carrot family. These species include; Wild carrot (daucus carota), Goutweed (aegopodium podagraria), poison hemlock (conium maculatum), water-parsnip (sium suave), spotted water-hemlock (cicuta maculata) and angelica (angelica atropurpurea). Once again, its "giant" size is the easiest distinguishing feature, as it towers above these other species. (View: Hogweed.look.alikes.pdf)



Human Health Issues


Giant hogweed can be a serious health hazard for humans. Its watery, clear sap contains photosensitizing compounds (furanocoumarins), which, when in contact with human skin and in combination with UV radiation, can cause burning. Content varies depending on plant part, but contact should be avoided at all times. The reaction of the skin depends on individual sensitivity. After 24hrs, reddening and swelling of the skin can be noticed, which is followed by an inflammatory reaction after 3 days. Depending on individual sensitivity, effects can last for months and skin can remain sensitive to UV light for years. Research has also shown that furanocoumarins in general may be carcinogenic and teratogenic.

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