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Giant hogweed: The facts

You may have recently heard about the dangers of giant hogweed – a non-native invasive plant which can cause burns – so we’ve put together the facts for you. Read on for everything you need to know.

What is giant hogweed?

Giant hogweed (Heracleum mantegazzianum) is a plant in the Apiaceae family which was introduced to the UK as an ornamental garden plant. It has white flowers and deeply incised compound leaves (where the leaf is divided into several smaller leaflets) whose edges are irregular and very sharply or jaggedly cut. It looks similar to its relative common hogweed however it can grow up to 5.5 metres (18 feet) in height, making it easy to spot when fully grown!

Giant hogweed is closely related to carrots, common hogweed, cow parsley, and (a bit confusingly!) is sometimes known as cow parsnip, or wild rhubarb.

Giant hogweed

What are the dangers?

Some people are concerned about recent stories regarding burns caused by giant hogweed. The sap of giant hogweed contains furocoumarin, which makes skin extremely sensitive to sunlight (phytophotodermatitis). If the sap gets onto your skin, then you are exposed to sun, your skin can blister badly and blistering can reoccur over months and even years.

Do I need to worry?

Hogweed stalk

Whilst it is true that the plant’s sap can indirectly cause serious burns, it’s important to remember that many of our most popular wild and garden flowers are toxic, such as foxgloves, bluebells and even daffodils. The best way to avoid injury is to familiarise yourself with the plant so that you can avoid the dangers. Just as you wouldn’t touch foxgloves then put your fingers in your mouth, it’s important to avoid brushing through patches of giant hogweed and exposing yourself to plants which have been cut which might cause you to get sap on your skin.

If you do get giant hogweed sap on your skin, be sure to wash the area thoroughly immediately, seek medical advice, and do not expose the area to sunlight for a few days.

How common is it?

In the UK it is an offence to grow or plant giant hogweed in the wild, but it has escaped gardens and parks and become fairly widespread throughout the country – particularly in Scotland, the north of England, and along riverbanks. To familiarise yourself with it and differentiate it from its harmless relatives, follow these tips:

Telling it apart from lookalikes

Giant hogweed

Giant hogweed

Chunky, bright green stems often with purple/red spots or blotches. The hollow leaf stalks are reddish, hollow and hairy. The leaves are divided into smaller leaflets and are very jagged and sharp. Leaves can grow to a massive 1–1.7 m (3 ft 3 in–5 ft 7) in width. Flowers appear in a flat-topped cluster which can be 80cm (31 inches) across.

Common hogweed

Common hogweed (Heracleum sphondylium)

This is very similar-looking to giant hogweed but is much smaller. Its stems aren’t blotchy like those of giant hogweed (their colour graduates smoothly from green to purple) and are ridged, hollow and hairy. This plant only reaches a maximum height of 2 metres (6 ft 7 in) and the symmetrical flower heads only reach 20cm across. Its seeds are much smaller and lighter than those of giant hogweed, and the leaves are less jagged and more rounded at the edges than giant hogweed.

Cow parsley

Cow parsley (Anthriscus sylvestris)

This is a native plant in the same family as hogweed. It grows to 60–170 cm (24–67 in) and also has clusters of white flowers. The leaves are very different to hogweed - they are tripinnate (the leaflets are themselves divided and then these divisions are divided again). Confusingly, some people refer to giant hogweed as giant cow parsley!

Ground elder

Ground elder (Aegopodium podagraria)

This is another non-native plant which has made its way into the environment. It is not related to elder trees (Sambucus nigra) but gets its name from having very elder-like leaves (meaning its leaves are very different to hogweed, although it has similar flat-topped clusters of small white flowers which can grow to 20cm across).