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Overview
Short description of Heracleum mantegazzianum, Giant Hogweed
Aptly named ‘giant’, this umbellifer (member of the cow-parsley family) has flowering stems typically 2-3 m high bearing umbels of flowers up to 80 cm in diameter. The basal leaves are often 1 m or more in size.
Description of Heracleum mantegazzianum, Giant Hogweed status in GB
Giant hogweed is widespread in lowland GB, and is invasive by lowland rivers and on waste land.
It is especially abundant by lowland streams and rivers, but also occurs widely on waste ground and in rough pastures. It grows on moist fertile soils, achieving its greatest stature in partial shade. In more open grassland, flowering may be delayed by repeated grazing.
First recorded in the wild in 1828 in Cambridgeshire.
Pathway and Method
Introduced to gardens as a monumental curiosity by 1820, and was deliberately planted by rivers and ponds.
Species Status
Widespread and well established in lowlands across England, Scotland, Wales and Northern Ireland. Has been spreading rapidly, despite control measures.
The species reproduces entirely by seeds; fruits are oval-elliptical broadly winged mericarps (6-18 Ć 4-10 mm), which are dispersed by wind, water and humans.
Reproduction
The species is monocarpic, that is, it reproduces only once in its lifetime. Plants are able to self-fertilize. A single plant produces about 20,000 seeds which have to be stratified in the soil in cold and wet conditions during winter and then are highly germinable.
Known Predators/Herbivores
Insect or pathogens have little effect. Grazing by livestock can significantly decrease the reproductive output but also prolong the lifespan before flowering.
Resistant Stages
Seeds form a short-term persistent seed-bank; the majority of them germinate the following year after release and only about 1% of seeds are able to survive more than 3 years in the soil.
Known Introduced Range Covers temperate Europe (with distribution clearly biased towards central and northern part of the continent) and parts of North America. Other invasive relatives, H. sosnowskyi and H. persicum, occur in northern and eastern European countries.
Impacts: Heracleum mantegazzianum, Giant Hogweed
Environmental Impact
The species may form dense stands reducing species diversity.
Health and Social Impact
The plant produces phytotoxic sap. The sap contains photosensitizing furanocoumarins, which in contact with human skin and combined with UV radiation cause skin burnings. The intensity of the reaction depends on individual sensitivity. The danger to human health complicates eradication efforts.
Economic Impact
It has not been defined but it clearly lowers the recreational value of the landscape due to human health risk.
