Its stems pictured at top left are green with purple blotches and white hairs. Giant hogweed originates from the Caucasus Mountains between the Black and Caspian seas by Russia - but it made its way to the U.
Birds and waterways can carry seeds, which can grow up to 10 years once they're dropped off. Giant hogweed sap contains toxic chemicals known as photosensitizing furanocoumarins. When these chemicals come into contact with the human skin, it can cause a skin reaction that's extremely sensitive to light.
The light-sensitive skin reaction causes dark painful blisters that form within 48 hours, and result in scars that can last anywhere from a few months to six years. Information on how to distinguish these giant hogweed wannabees from the real thing can be found later in this profile.
Giant hogweed is a perennial herb with tuberous root stalks. It survives from one growing season to another by forming perennating buds surviving from season to season and enduring a period of dormancy during the winter. Numerous up to , , half inch long, winged, flattened oval seeds form in late-summer. These seeds, originally green, turn brown as they dry and can be spread by animals, surface runoff of rain, or on the wind, establishing new colonies.
Seeds can remain viable in the soil for up to 10 years. The plant may grow to 15 to 20 feet in height. As mentioned earlier, there are several plants in New York and the Northeast that can be mistaken for giant hogweed. Key features for distinguishing these plants from giant hogweed are explained below. Click the identification tables to enlarge. Giant hogweed may grow to 15 to 20 feet in height. Stems are 1 to 3 inches in diameter, but may reach 4 inches.
Stems are marked with dark purplish blotches and raised nodules. Leaf stalks are spotted, hollow, and covered with sturdy bristles most prominent at the base of the stalk. Stems are also covered with hairs but not as prominently as the leaf stalks. Leaves are compound, lobed, and deeply incised; can reach up to 5 feet in width. Numerous white flowers form a flat-topped, umbrella-shaped head up to two and a half feet across.
Native Cow parsnip, while resembling giant hogweed, grows to only five to eight feet tall. The deeply ridged stems can be green or slightly purple, do not exhibit the dark purplish blotches and raised nodules of hogweed, and only reach one to two inches in diameter, contrasted with hogweed stems which can reach three to four inches in diameter.
Where giant hogweed has coarse bristly hairs on its stems and stalks, cow parsnip is covered with finer hairs that give the plant a fuzzy appearance. Both sides of the leaves exhibit these hairs but they are predominantly on the underside of the leaves.
Native purple-stemmed Angelica is more easily differentiated from giant hogweed by its smooth, waxy green to purple stems no bristles, no nodules , and its softball-sized clusters of greenish-white or white flowers, seldom reaching a foot across. As with cow parsnip, Angelica is much shorter than giant hogweed, usually no more than eight feet tall. The flowers are also white but flat-topped and no larger than one foot wide.
The stem is usually green, but it can have purple marks that are not spots. Ellis, University of Connecticut, Bugwood. Mehrhoff, University of Connecticut, Bugwood.
Means of spread and distribution It spreads by seed that can be moved by wind, water, wildlife, and humans. Prevention and management Management of giant hogweed requires careful handling and appropriate personal protective equipment.
For all management methods, it is important to monitor the site for several years after treatment for newly germinating seedlings or resprouting roots. Removing plants by hand is difficult, and dangerous considering the toxic nature of the plant's sap. Mowing can be a good management tool, if repeated throughout the season and over several years, or in coordinated conjunction with herbicide application.
Well-timed herbicide application can be effective, but numerous applications are usually required. If using herbicide treatments, check with your local University of Minnesota Extension agent , co-op, or certified landscape care expert for assistance and recommendations. Giant hogweed is not native to the UK. It originates from the Caucasus Mountains and Central Asia. It was first introduced to the UK as an ornamental in the 19th century where it escaped and naturalised in the wild.
It can now be found throughout much of the UK, especially colonising river banks where its seeds are transported by the water. Giant hogweed looks like an enormous cow parsley. When it's fully grown, it can reach towering heights of between 1. It forms a rosette of jagged, lobed leaves in the first year before sending up a flower spike in the second year and then setting seed. Stems: green with purple blotches and stiff, white hairs.
Stems are hollow with ridges and have a thick circle of hairs at base of each leaf stalk. Leaves: huge, up to 1. It looks a bit like a rhubarb leaf, with irregular and very sharp or jagged edges - which has given rise to one of its other common names - wild rhubarb. The underside of the leaf is hairy.
Flowers: appear in June and July.
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