I received Wisconsin’s “Natural Heritage Conservation Program 2016 Annual Report” (page 10) last week and was pleased to see that the noxious weed Giant Hogweed (Heracleum mantegazzianum) has either been eradicated or under control in all known sites. Whew! Much like Wild Parsnip (Pastinaca sativa), Giant Hogweed is phototoxic; if one touches it and then exposes that touched area of the skin to sun, it can cause 3rd degree burns and months of convalescing.
Giant Hogweed is a very tall plant, reaching 15 feet or more and has leaf and flower characteristics similar to our native Cow Parsnip (Heracleum sphondylium) and Angelica (Angelica atropurpurea). But both of these native plants only reach four to eight feet tall and their leaves are one-fifth the size of Giant Hogweed. Also, while Cow Parsnip has a green stem and Angelica has a red stem, Giant Hogweed has dark purple spots on its stem. Be sure to check closely, but carefully before you touch.
All like moist, rich soil and can grow in sun to partial shade.
To read the complete information gathered by the Special Assessment Group before classifying Giant Hogweed as a prohibited invasive species, go to literature review.
To learn more about Wisconsin’s noxious weeds classifications see NR 40.