www.nonnativespecies.org Produced by Olaf Booy, Max Wade and Vicky White of RPS
Giant Hogweed Species Description Scientific name: Heracleum mantegazzianum AKA: Efwr enfawr (Welsh) Native to: Caucasus mountains in south west Russia and Georgia Habitat: Widespread, most common on river banks Easy to identify when fully grown by height, size of leaves and size of flowers. Can be confused with native hogweed when not fully grown or when growth is stunted (e.g. regrowth after cutting). Introduced as an ornamental. First recorded wild in the UK in the late 19th century. Spreads solely by seeds, mainly through deliberate planting, wind dispersal and in water courses. Now common across much of the UK. Contact with any part of this plant must be avoided as even minute amounts of sap can cause blistering of the skin following exposure to sunlight. Other negative impacts include out-competing native flora, river bank erosion and increase in flood risk. Can cause delays/ additional costs on development sites where the plant must be removed as controlled waste in order to comply with legislation. Giant hogweed is listed under Schedule 9 to the Wildlife and Countryside Act 1981 with respect to England, Wales and Scotland. As such it is an offence to plant or otherwise cause this species to grow in the wild. Under the Environmental Protection Act 1990, giant hogweed is also classified as controlled waste. For details of legislation go to www.nonnativespecies.org/legislation.
Blotchy or rarely continuous purple
Up to 80cm
Umbrella shaped flower
o Up t
Up to 5m
3m
Sharply divided / serrated leaves
Flower white or rarely pinkish
Bristles on underside Stems usually with sharp bristles
Up to 50,000 seeds per plant held on seed head
1.5 cm
Key ID Features
Stem 5-10cm diameter
Seeds have dark stripes (oil ducts) 2 on one side, 4 on the reverse
Identification throughout the year
Winter Summer
Spring
Hogweed flowers heads are much smaller, up to 15cm
1cm
Key differences between hogweed and giant hogweed include the height, width of stem, size of leaf, size of flower head and size of seed.
Up to 2m
Comparison of stems
Hogweed Giant Hogweed Comparison of leaves
Native (Heracleum sphondylium)
Giant Hogweed
Comparison of seeds 1cm
Hogweed
Giant Hogweed
Hogweed
2m
Hogweed
Distribution Widespread and common across much of the UK. Extensive infestations are found particularly in Scotland and the north of England. Less abundant in Cornwall. Often associated with large rivers. Source: NBN Gateway. Check website for current distribution
When in full height it is difficult to confuse giant hogweed with any other plant. While still growing or stunted, possibly as a result of disturbance, it can be confused with some other native plants. The most likely species with which it might confused is hogweed.
Similar Species
References and further reading: Blamey, M, Fitter, R and Fitter, A (2003) “The Wild Flowers of Britain and Ireland. The Complete Guide to the British and Irish Flora.” A & C Black Booy, O and Wade, P M (2007) “Giant Hogweed Management in the United Kingdom”. RPS Group plc Pyšek P, Cock, M J W, Nentwig, W & Ravn, H P (2007) “Ecology and Management of Giant Hogweed (Heracleum mantegazzianum)”. CAB International Stace, C (1999) “Field Flora of the British Isles”. Cambridge University Press Photos from: Olaf Booy, Steve Smith, Vicky White