Himalayan Balsam - Impatiens glandulifera

Also known as Indian Balsam, this species was introduced to Britain from the Himalayas as a garden plant in 1839, establishing in the wild by 1855.

Habitats

It grows mainly on river and stream banks in dense patches, as well as in wet woodlands and on waste ground.

Description

Himalayan Balsam is easily recognisable as it grows up to 2m in height making it one of the tallest annual plants in Britain. Its fleshy hollow stems are red and bear toothed leaves 6-15 cm long in whorls; these leaves are dark green, lance-shaped and often have reddish margins. Sweetly scented flowers are borne between June and October; these are 2-4cm long and scented, usually in various shades of pink or purple or white. The flowers have the shape of a helmet giving it the nickname of ‘Policeman’s Helmet’.

Biology

In the autumn each plant produces many large green pods, which explode at the slightest touch when they are ripe, thus violently casting the seeds into surrounding habitats. Seeds are viable for many months and float, so it is readily dispersed downstream along river and stream corridors.

Because the flowers produce a large amount of nectar over a long period of time they are attractive to many insects - particularly bumblebees - that can cause reduced local pollination of native plants. Himalayan Balsam competes with native plants for space and other natural resources, and is problematic on riverbanks when it dies down in autumn leaving banks bare of vegetation and thus more vulnerable to erosion during periods of spate. By dispersing it seeds widely (each plant can produce over a thousand seeds), the seeds are spread widely in flowing water and are viable for many months.

Control 

Himalayan Balsam is widely regarded as an undesirable though attractive invasive species, and targeted measures are usually made to eradicate it rather than conserve it. It has spread widely in the wild since its original introduction and is now one of our most familiar invaders.

The Wiltshire Wildlife Trust's Wessex Chalk Streams Project is taking a lead in recording the presence of non-native invasive plants identified as a significant threat to the characteristic species and habitats of the River Avon. Click here to find out more