People in the Portsmouth area are being warned to be extra vigilant after a number of reports of the toxic giant hogweed across the UK in the last couple of weeks.
There have been sightings in the Midlands, Greater Manchester, Scotland and Northern Ireland.
The plant grows very quickly and contains chemicals known as photo-sensitising furanocoumarins.
These substances prevent the body from protecting itself from UV light and can lead to severe burns.
A red rash develops on the skin, which grows more painful and then blisters.
Guy Barter of the Royal Horticultural Society said: “Wherever you live in the UK, you can expect to encounter this plant”.
Paul Cook, curator at RHS Garden Harlow Carr in Harrogate, points out that in some places it’s on the increase. “You tend to find it in less accessible places,” he says.
“In some parts of the county it’s increasing and in others, where it’s been controlled, it’s going down.”
It’s attractive appearance can lull unsuspecting people who stumble across it into a false sense of security. “It’s very distinctive but a lot of people have forgotten just how horrible it can be,” said Paul.
Those who encounter Giant Hogweed certainly don’t forget it in a hurry.
Wherever you live in the UK, you can expect to encounter this plantGuy Barter, Royal Horticultural Society
“When the sap or juice from the stem comes into contact with the skin it can cause intense irritation, particularly in the sunny weather.
“It doesn’t last very long but it can feel like you’re skin is being burned.”
The facts: what does it look like
Giant hogweed (Heracleum mantegazzianum) is a close relative to cow parsley.
It has thick, bristly, reddish-purple stems and can reach over 3m (10ft) in height.
The flowers are white in a flat-topped clusters that can be as large as 60cm (2ft) across.
Giant hogweed was originally brought to Britain from Central Asia in 1893.
It commonly grows on riverbanks and wasteland.
Its leaves, stems, roots, flowers and seeds contain toxic components which can be transferred by contact and make exposed skin extremely sensitive to sunlight.
What to do if you come into contact
After coming into contact with the plant, the burns can last for several months and the skin can remain sensitive to light for many years.
NHS advises: “If the sap of the giant hogweed comes into contact with your skin, it can cause severe, painful burns and make your skin sensitive to strong sunlight.
“If you touch a giant hogweed, cover the affected area, and wash it with soap and water.
“The blisters heal very slowly and can develop into phytophotodermatitis, a type of skin rash which flares up in sunlight. If you feel unwell after contact with giant hogweed, speak to your doctor.”
*Have you been affected by hogweed? Ring the newsdesk on (023) 9262 2118