Heracleum mantegazzianum

Giant Hogweed
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Asterids
Order:	Apiales
Family:	Apiaceae
Genus:	Heracleum
Species:	H. mantegazzianum
Binomial name
Heracleum mantegazzianum Sommier & Levier

Giant Hogweed (Heracleum mantegazzianum, also giant cow parsley) is a plant in the family Apiaceae, native to the Caucasus Region and Central Asia. It may reach 2–5 metres (rarely to 7 m) tall. Except for size, it closely 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.

It is further distinguished by a stout, dark reddish-purple stem and spotted leaf stalks that are hollow and produce sturdy bristles. Stems vary from 3–8 cm in diameter, occasionally up to 10 cm. The stem shows a purplish-red pigmentation with raised nodules. Each purple spot on the stem surrounds a hair, and there are large, coarse white hairs at the base of the leaf stalk. The plant has deeply incised compound leaves which grow up to 1-1.7 m in width.

Giant Hogweed is a short lived perennial (lasting typically between 5-7 years) 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 (2.5 ft) 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. After seeds have set the individual plant dies. Plants in earlier stages of growth die down in the autumn. Tall dead stems may mark its locations during winter.

Many foreign plants were introduced to Britain in the 19th century, mainly for ornamental reasons. A few have become aggressively dominant, creating serious problems in some areas. It is now widespread throughout the British Isles especially along riverbanks. By forming dense stands they can displace native plants and reduce wildlife interests. It has also spread in the northeastern and northwestern United States and central and eastern Canada. It is equally a pernicious invasive species in Germany, France and Belgium, overtaking the local species. It was introduced in France in the 19th century by botanists, much appreciated by beekeepers.

Phototoxicity

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 UV-rays. Initially the skin colours red and starts itching. Then blisters form as in burns within 48 hours. They form black or purplish scars that can last several years. Hospitalisation may be necessary. Presence of minute amounts of sap in the eyes can lead to temporary or even permanent blindness. 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. In Germany, where this plant has become a real nuisance, there were about 16,000 victims in 2003.

Children should be kept away from Giant Hogweed. Protective clothing, including eye protection, should be worn when handling or digging it. If skin is exposed, the affected area should be washed thoroughly with soap and water and the exposed skin protected from the sun for several days.

Natural Predators

The USDA Forest Service states that pigs and cattle can eat Giant Hogweed without apparent harm.

Countermeasures

Because of its phototoxicity and its 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.

It is also a common plant in marshy areas of Ireland although the extent of its dangers is not commonly known there.

Hogweed is regulated as a federal noxious weed by the U.S. Government, and is therefore illegal to import into the United States or move interstate without a permit from the Department of Agriculture.

Cultural references

On their 1971 album Nursery Cryme, Genesis has a song called "The Return of the Giant Hogweed". The song presents a time when the Giant Hogweed poses a menace of apocalyptic proportions, threatening the human race.

See also

• Hogweed Full plant family list
• Other Europe invasive species Heracleum sosnowskyi and Heracleum persicum
• Native Europe hog weeds Heracleum sphondylium and Heracleum sibiricum
• Species that can be mistaken for tall invasive hogweeds Wild Parsnip, Garden Angelica, Wild Angelica

External links

• Identifying and removing Giant hogweed on NetRegs.gov.uk
• InvadingSpecies.com - advice from Ontario, Canada
• Contact-Poisonous Plants of the World
• Photos of Giant Hogweed
• Manual for eradication of Giant Hogweed - available for download as pdf
• Environment Agency of Finland: Photo of the blisters caused by the plant (Graphic)
• Stuff.co.nz: Warnings after children burnt by garden plant
• it:Panace di Mantegazzi
• The Knotweed Company
• Species Profile- Giant Hogweed (Heracleum mantegazzianum), National Invasive Species Information Center, United States National Agricultural Library. Lists general information and resources for Giant Hogweed.