Invasive giant hogweed in Britain

This video is called ‘Poisonous Plants 1-2-1′ Heracleum mantegazzianum, giant hogweed.

The beast in the beautiful giant hogweed

Friday 7th August 2015

An invasive plant, first introduced to Britain by aristocratic garden owners, is now seriously disturbing the delicate balancing act that is our native flora, says PETER FROST

Many of the tabloid papers have been carrying lurid stories of a Russian giant over 12ft tall attacking people on canal towpaths all across England. Sadly this time they are true.

The plant, giant hogweed (Heracleum mantegazzianum), a native of the Caucasus mountains, has many aliases such as cartwheel-flower, giant cow parsnip, hogsbane or giant cow parsley. Children might call it giant rhubarb or simply a triffid.

This plant is phototoxic and its sap causes phytophotodermatitis in humans, resulting in blisters, long-lasting scars and if the eyes are affected blindness, sometimes permanent.

The worse cases, which can result in hospitalisation and have even been known to be fatal, occur only when exposure to the sap is combined with long periods in bright sunshine. On cloudy days irritation from the sap is usually much milder or even non-existent.

The recent bright sunny summer days with in some cases record temperatures and hours of sunshine are the real culprit in the recent crop of headline-making cases.

Perhaps because of its size, or its rigid huge hollow stems, children find the plant fascinating. They use the stems as toy telescopes or peashooters. The former gets sap in the eyes the latter in the mouth and lips.

Giant hogweed can grow as much as 18ft high although between six and 12ft is more normal.

Full-grown plants are hard to mistake for anything else but smaller immature plants can be misidentified as common hogweed (Heracleum sphondylium), garden angelica (Angelica archangelica) and many other similar lacy-flowered umbrella-shaped common towpath and wasteland plants.

Key clues to accurate giant hogweed identification are stout, brightgreen stems and leaf stalks frequently with dark red or purple spots and sturdy bristles. The hollow stems can vary from an inch to three inches in diameter.

Giant hogweed is biennial, usually flowering in its second year from late spring to mid-summer, with numerous white flowers clustered in an umbrella-shaped head 2-6ft in diameter.

A single plant can produce 100,000 seeds. It is illegal to plant or transplant the species but the giant hogweed doesn’t know that.

Like so many of our unwelcome invasive species it was first introduced by aristocratic garden owners importing exotic-looking plants from all over the globe with no thought of disturbing the delicate balancing act that is our native flora and fauna.

To grace their expensive estates they imported exotic species such as grey squirrels and various small deer including the notorious muntjac.

In the plant world perhaps the biggest environmental disaster was the importing of Rhododendron ponticum, which has become a vast problem in the woodlands of the west highlands of Scotland, in Wales and on heathlands in southern England.

The huge plants spread by suckering and crowd out our more delicate native flora.

Massive clearance strategies have been developed, including the flailing and cutting-down of plants with follow-up herbicide spraying. But in reality this beautiful but unwelcome species seems to be winning the battle in most places.

Three huge and out-of-scale plants, giant hogweed, gunnera, and Japanese knotweed — are all common escapees and have the size and stature to turn our rivers and canal banks into a passable replica of an Amazonian jungle.

Children need to be kept away from giant hogweed and warned about its dangers. Adults cutting or uprooting plants should wear protective clothing including eye protection and stout gloves.

If sap does get on the skin the affected area should be washed thoroughly with soap and water and the exposed skin protected from the sun for several days.

If blisters do start to develop seek urgent medical attention.