Giant Hogweed

Heracleum mantegazzianum
Other name: Giant Cow Parsnip
Family: Apiaceae

This spectacular plant (a member of the Umbellifer family) was introduced from the Ural Mountain region by Victorian gardeners. Unfortunately it is now widespread in the wild and causes a number of problems. The stems contain copious amounts of clear watery sap which makes the skin very sensitive to sunlight. On contact the skin can become broken and blistered. It can also cause temporary blindness if it gets into the eye. The leisons appear some hours after contact, heal slowly and can leave the skin permanently sensitised to sunlight - Phytophotodermatitis

It is also a threat to native plants as it colonises riverbanks and other disturbed ground in dense stands blocking out light with its large leaves.

It is a perennial which dies away in the late autumn and comes into growth the following spring. The hollow stems can be 10 cm thick and carry the plant to a height of 3 to 5 metres. They are covered in fine hairs which can cause irritation on contact with the skin. The leaves are compound with 3 leaflets and the lower ones can be up to 1.5 m across on a long, spiny stalk.

The small, white flowers are carried on flat, multi-branched umbels and develop eliptical seed which are 7 to 12 mm long. A single flower head can produce 1500 seed and they can remain viable in the soil for 7 to 8 years.

Under the 1981 Wildlife and Countryside Act/ Wildlife (Northern Ireland) Order 1985, it is an offence in the UK to allow it to grow in the wild. To dispose of any plant material or soil contaminated with it, requires a certificate for Waste Transfer and to be taken to a suitably licensed landfill site.

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