Himalayan Balsam (Impatiens glandulifera) is another horticultural specimen that was introduced in the 19th Century, 1839 to be precise that has since escaped to become nuisance in the wild.
It is the tallest annual in the UK growing up to 3 metres and is an attractive plant with a distinctive purple pink flower, which has led to the slang name of ‘Policeman’s helmet’.
Each plant can produce up to 800 seeds which are explosively released when the seed pods are mature, capable of projecting the seeds 7 metres. This is a highly effective dispersal method which enables the plant to rapidly colonise the damp and riparian habitats that the plant favours. The seeds may be further spread by water and can remain viable for 2 years.
It is a threat to biodiversity out competing native species and monopolising local environments. On riverbanks, once it has died back, the area is vulnerable to erosion in the winter.