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Giant Hogweed

©Eva Ekeblad

Giant hogweed

As its name suggests, giant hogweed it a large umbellifer with distinctively ridged, hollow stems. An introduced species, it is an invasive weed of riverbanks, where it prevents native species from growing.

Scientific name

Heracleum mantegazzianum

When to see

June to August

Species information

Statistics

Height: up to 5m
Invasive, non-native species.

About

Giant hogweed was introduced into the UK by the Victorians as an ornamental plant for lakesides and gardens. It escaped into the wider countryside and gained notoriety in the 1970s as an alien species that favours damp spots like riverbanks. At this time, many children started to display blisters as a result of touching the plant's sap while using the stems to make pea-shooters or telescopes: sunlight makes the skin sensitive to the irritants in the plant, causing the skin to redden. Today, it is widely acknowledged that neither gardeners nor conservationists should attempt to cut the plant down (exposing its sap) as its toxins can cause serious, recurring skin damage.

How to identify

Giant hogweed is an immensely tall umbellifer (member of the carrot family) that displays large, white, umbrella-like clusters of flowers. Its hollow stem is ridged and purple-spotted, and its leaves are large and divided.

Distribution

Scattered distribution throughout the UK.

Did you know?

Its favoured position by the banks of rivers allows giant hogweed the perfect opportunity to expand as it sends its seeds into the water to be dispersed by its flow. Each plant can produce 30-50,000 seeds each year and colonies can quickly overtake a habitat, crowding out native plants.