Himalayan balsam is not native to the UK and was introduced from the western Himalayas in 1839 as a garden ornamental. It has since escaped and spread across the country. Himalayan balsam is an annual plant, growing from seed set the previous year. This seed germinates early in the spring and grows rapidly to form dense stands up to 3 m in height which shade out native vegetation. It is the tallest annual plant in Britain. It has hollow, jointed pinkish-red stems which are sappy and brittle. The leaves are shiny, dark green and spear-shaped with a dark red midrib and up to 150 mm long. The flowers which appear between June and October are fragrant, purplish-pink, slipper shaped and held on long stalks. The numerous seeds are widely scattered by an explosive seed capsule, and can travel along water ways into new areas. When the plant dies back in the autumn it leaves bare patches which cause particular problems along riverbanks which become prone to erosion.
The plant is now quite widespread in central and eastern Norfolk and is still expanding its range. It can be seen along the banks of rivers, in wet woodland and on waste ground.