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Giant Hogweed
(Heracleum mantegazzianum)

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Invasive Status
Invasive Population increasing
Natural Range
  • Caucasus
Introduced Range
  • West and central Europe
  • Iceland
  • Some parts of USA
  • Some parts of Australia
  • New Zealand
Pathways
Public gardens
Issues

Phototoxic sap

Shadowing native species

Removal Methods

Active removal by digging up plants

Active removal by cutting back plants 

Grazing livestock

Giant hogweed (Heracleum mantegazzianum) is a very large member of the parsley and carrot family Apiaceae, growing up to 5 metres (16 feet) tall. It can be a threat to health due to its phototoxic sap, and so should be avoided, especially from contact with bare skin.

RangeEdit

Native rangeEdit

The giant hogweed is native to the Caucasus region in the Midle East. It can be found in Georgia, Iran and Turkey.*

Introduced RangeEdit

The species was first introduced to Europe. Here, it is present in each Scandinavian country, south to Hungary through the Baltic States, European Russia, Poland and Slovakia. It's range soreads east to France, Ireland, UK and Denmark as well as all the countries in between (Austria, Czech Republic, Germany, north Italy. Liechtenstein, Switzerland, Belgium and the Netherlands). It can also be found in Iceland.*

In North America, this species is present in southern Canada (especially to the southwest), as well as various states in the USA. It can be found from Maine to Washington via Pennsylvania, as well as being found in the lakeside states of Michigan, Indiana and Illinois, in Florida and finally in Oregon.*

Giant hogweed has also been brought to Australia, in South Australia and Tasmania, as well as in New Zealand.*

Pathways and IntroductionEdit

Giant hogweed is introduced as an ornamental plant and then proliferates and spreads. This introduction method has occurred several times for this species.*

Giant hogweed's introcution to Europe is mostly recorded. In the UK, the species was sold as seed from Kew Botanical Gardens and had naturalised in Cambridgeshire by 1828. It had been recorded in the Netherlands, Switzerland, Germany, Ireland, Denmark and the Czech Republic by 1862. Since then, it has spread. The latest European introductions were recorded in Slovakia and in Iceland around 1945.*

ImpactsEdit

The giant hogweed's watery sap is phototoxic and contains furanocoumarins. These cause the skin to become extremely sensitive to sunlight, resulting in a condition called phyto-photodermititis which involves reddening, burning and blistering of the skin. These effects can last for several months, with the skin remaining sensitive to light for years.** 

The plant's dangerous phototoxic nature can result in the closure of public areas. Additionally, the leaves may be harmful to waterfowl. The plant outcompetes native plant species, largely by shadowing them with its large leaves. There could also be sedimentation impacts on fish. During cold winters, the plants die back, leaving riverbanks vulnerable to erosion.***

Control and Removal MethodsEdit

Active removal of the plants is often used. Caustion is taken not to touch the plants with bare skin, and so protective clothing is worn. Whole plants are removed in the soil or, if this is not possible, the stems are cut at an angle below the surface and the surrounding soil is mulched. Return trips are then made to the site to ensure no new saplings are able to grow.****

Hogweed is also being removed more passivley using livestock which aren't affected by the sap.^/^^

SourcesEdit

 * Invasive Species Compendium

** GB NonNative Species Secretariat - Dangers of Giant Hogweed

*** Invasive Species Ireland

**** Sea to Sky Invasive Species Council

^ ConservationEvidence.com: "Longterm sheep grazing successfully eradicates giant hogweed Heracleum mantegazzianum from a grassland at Lake Furesø, West Zealand, Denmark"

^^ BBC News: "Blackface sheep winning giant hogweed battle"