IUCN threat status:

Least Concern (LC)


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Heracleum mantegazzianum

Heracleum mantegazzianum, commonly known as giant hogweed,[1][2][3] cartwheel-flower,[1][2][3] giant cow parsnip,[4][5]"hogsbane" or giant cow parsley,[6] is a plant in the family Apiaceae. In New Zealand it is also sometimes called wild parsnip,[2] or wild rhubarb,[2] It typically grows to heights of 2–5.5 m (6 ft 7 in–18 ft 1 in).[7] Superficially, it resembles common hogweed (Heracleum sphondylium), Heracleum sosnowskyi or garden angelica (Angelica archangelica). It is phototoxic and considered to be a noxious weed in many jurisdictions. Giant hogweed is native to the Caucasus Region and Central Asia. It was introduced to Britain as an ornamental in the 19th century, and it has also spread to many other parts of Europe, the United States and Canada.

The sap of giant hogweed causes phytophotodermatitis in humans, resulting in blisters, long-lasting scars, and—if it comes in contact with eyes—blindness. These serious reactions are due to the furocoumarin derivatives in the leaves, roots, stems, flowers, and seeds of the plant.


Giant hogweed has a stout, bright green stem that is frequently spotted with dark red and hollow red-spotted leaf stalks that produce sturdy bristles. The hollow stems vary from 3–8 cm (1.2–3.1 in) in diameter, occasionally up to 10 cm (3.9 in). Each dark red spot on the stem surrounds a hair, and large, coarse white hairs occur at the base of the leaf stalk. The plant has deeply incised compound leaves which grow up to 1–1.7 m (3 ft 3 in–5 ft 7 in) in width.

Giant hogweed is a short-lived perennial (lasting typically between five and seven years),[citation needed] with tuberous rootstalks that form perennating buds each year. It flowers in its final year from late spring to mid summer, with numerous white flowers clustered in an umbrella-shaped head that is up to 80 cm (31 in) in diameter across its flat top. The plant produces 1,500 to 100,000 flattened, 1 cm long, oval dry seeds that have a broadly rounded base and broad marginal ridges. The plants are monocarpic, dying after they have set seed. Plants in earlier stages of growth die down in late autumn or early winter. Tall dead stems may mark its locations during winter.

Introduction to Western Europe and North America[edit]

Distribution of giant hogweed in Europe (2005)

Giant hogweed was among many foreign plants introduced to Britain in the 19th century, mainly for ornamental reasons. It is now widespread throughout the British Isles, especially along riverbanks. By forming dense stands, they can displace native plants and reduce wildlife interests.[8] It has also spread in the northeastern and northwestern United States and southern Canada. It is equally a pernicious invasive species in Germany, France and Belgium, overtaking the local species.[8] It was introduced in France in the 19th century by botanists, where it is much appreciated by beekeepers.

In Canada, the plant has been sighted in British Columbia, Alberta, Saskatchewan, Ontario, Quebec, New Brunswick, Nova Scotia and in isolated areas of Newfoundland. It has been seen in Quebec since the early 1990s.[9] The plant's spread in Ontario began in the Southwest and was seen in 2010 in the Greater Toronto Area and Renfrew County near Ottawa.[10]

The native cow parsnip, Heracleum maximum, very common in Newfoundland and northern Ontario, is often misidentified as giant hogweed. Because of its similarity to cow parsnip, numerous false reports of giant hogweed are reported annually to local OMNR offices in Ontario. People who suspect that they have giant hogweed should confirm identification by checking the stems and comparing their plant with descriptions of cow parsnip. Giant hogweed stems are green with obvious purple blotches from which stiff white hairs arise. The native cow parsnip has green (usually) to purplish (rarely) stems that are ridged but unspotted, and covered with fine white hairs. Size is not a reliable trait to differentiate these two species, since cow parsnip, growing in a rich site, can reach 2+ metres [10–12 ft.] in height, while giant hogweed sometimes grows only to heights of 1.5 metres [7–8 ft.]. Giant hogweed flowering heads (compound umbels) also branch frequently, forming clusters of several flowering head 80+ cm [2.5 ft.] across.


Giant hogweed (close-up)

Giant hogweed is a phototoxic plant. Its sap can cause phytophotodermatitis (severe skin inflammations) when the skin is exposed to sunlight or to ultraviolet rays. Initially, the skin colours red and starts itching. Then blisters form as it burns within 48 hours. They form black or purplish scars that can last several years. Hospitalisation may be necessary.[8] Presence of minute amounts of sap in the eyes can lead to temporary or even permanent blindness.[11] These reactions are caused by the presence of linear derivatives of furocoumarin in its leaves, roots, stems, flowers and seeds. These chemicals can get into the nucleus of the epithelial cells, forming a bond with the DNA, causing the cells to die. The brown colour is caused by the production of melanin by furocoumarins.

Predators and countermeasures[edit]

Because of its phototoxicity and invasive nature, giant hogweed is often actively removed. In the UK, the Wildlife and Countryside Act 1981 makes it an offence to plant or cause giant hogweed to grow in the wild.[8][12] It is also a common plant in marshy areas of Ireland.

Hogweed is regulated as a federal noxious weed by the US government, and is therefore illegal to import into the United States or move interstate without a permit from the Department of Agriculture.[13] The USDA Forest Service states pigs and cattle can eat it without apparent harm.[5]

The New York DEC has had an active program to control giant hogweed since 2008, including reporting, database maintenance, and crews for removal or herbicide control.[14][15]

In 2011, Maine state horticulturists, describing the plant as "Queen Anne's lace on steroids", reported the plant has been reported at 21 different locations in Maine, with the number of plants ranging from one to a hundred.[16]

In popular culture[edit]

Heracleum mantegazzianum is the antagonist of the song "The Return of the Giant Hogweed" by the progressive rock group Genesis. The song is included on their album Nursery Cryme. The song heavily exaggerates on the actual events following the Hogweed introduction into Britain, and attributes the plant with intention and evil will towards mankind. Also featured on season 1, episode 1 Rosemary and Thyme, And No Birds Sing.

See also[edit]


  1. ^ a b John H. Wiersema. "USDA GRIN taxonmy". Ars-grin.gov. Retrieved 2013-08-06. 
  2. ^ a b c d "(New Zealand) National Pest Plant Accord 2008". 2008. Retrieved 2009-01-26. 
  3. ^ a b "Species Profile- Giant Hogweed (Heracleum mantegazzianum)". National Invasive Species Information Center, United States National Agricultural Library. 
  4. ^ "Giant Hogweed". the Ontario [Canada] Federation of Anglers & Hunters. 
  5. ^ a b "Giant hogweed" (PDF). Center for Invasive Species and Ecosystem Health. USDA/University of Georgia. Retrieved 2011-07-06. 
  6. ^ Thomas Forney, Glenn Miller, and Beth Myers-Shenai (2009). "Oregon Department of Agriculture Plant Pest Risk Assessment for Giant Hogweed Heracleum mantegazzianum". 
  7. ^ Stace, C.A. (2010). New flora of the British isles (Third ed.). Cambridge, U.K.: Cambridge University Press. p. 450. ISBN 9780521707725. 
  8. ^ a b c d see http://www.netregs.gov.uk/netregs/processes/367839/?lang=_e[dead link]
  9. ^ "5 things you need to know about toxic hogweed". CBC News. 
  10. ^ Halfnight, Drew (July 13, 2010). "Giant weed that burns and blinds spreads across Canada". The National Post. 
  11. ^ "Toxic weed discovered in Ottawa". CBC. 2010-07-13. Retrieved 2014-08-14. 
  12. ^ Wildlife & Countryside Act 1981 Section 14 and Schedule 9, Part II.
  13. ^ "Invasive and Noxious Weeds: Federal Noxious Weeds". Natural Resources Conservation Service. U.S. Department of Agriculture. 
  14. ^ "Giant Hogweed". NYS Dept. of Environmental Conservation. Retrieved 2011-07-06. 
  15. ^ "Beware of Giant Hogweed!". New York State Department of Environmental Conservation. Retrieved 2014-06-06. 
  16. ^ "State confirms poisonous plant sightings | The Portland Press Herald / Maine Sunday Telegram". Pressherald.com. 2011-08-01. Retrieved 2013-08-06. 

External links[edit]


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