Japanese Knotweed (scientific name Fallopia japonica) was introduced to the UK as an ornamental plant in the mid nineteenth century. It is a clump forming perennial weed typically found growing on riverbanks, roadsides, derelict wasteland and areas of disturbed soil. Its root system is extremely vigorous and can cause structural damage.

Japanese Knotweed can penetrate hard surfaces such as tarmac and has been known to penetrate through the foundations of houses. It often overtakes and replaces the native flora. It is illegal to cause the spread of this plant to new areas.

Himalayan or Indian Balsam (Impatiens glandulifera) is a native of the western Himalayas that was first introduced into Britain in 1839. Since then the plant has escaped into the wild and has rapidly colonised river banks and other areas of damp ground.

Himalayan Balsam grows in dense stands, suppressing the growth of native vegetation, and dies back in winter leaving river banks bare and liable to erosion.

Giant Hogweed

Giant Hogweed (Heracleum mantegazzianum) was introduced to the UK in the late nineteenth century as an ornamental plant. It is a perennial which is widespread in the UK, and typically found growing on riverbanks and areas of derelict wasteland. The plant is characterised by its size and can grow up to 5m tall with leaves up to 1m across. Growth starts in March and the plant can take 4 years to mature and flower.

Each plant can produce several thousand seeds, which remain viable for up to 15 years. The seeds may be dispersed by wind or water and may be carried on footwear, vehicles, or in contaminated soil. Because of its size and invasive nature, the plant can out compete native plant species. Giant Hogweed is also a potential danger to public health with the possibility of painful blistering and severe skin irritation from touching the poisonous sap found in hairs on the stems, edges and undersides of the leaves.

Floating Pennywort

Floating pennywort (Hydrocotyle ranunculoides) is a native of North America that was first brought to Britain in the 1980s as an ornamental plant for ponds and aquaria. H.ranunculoides grows in the shallow margins of slow flowing eutrophic watercourses, particularly ditches.

The plant forms a dense mat which block waterways affecting both their amenity and ecological value as well as contributing to the risk of flooding. Principal growth occurs in late summer when the plant can double its wet weight in less than 3 days.

Australian Swamp Stonecrop

Australian Swamp Stonecrop (Crassula helmsii, also known as New Zealand Pigmy Weed) was first introduced to Britain in 1911 from Tasmania. It is sold as an oxygenating plant for ponds and has now been found at over 1,500 wild sites in Britain.

Crassula can inhabit any static or slow flowing freshwater habitat up to 3m in depth, regardless of the water chemistry. Growth is rapid and continues throughout the year, absorbing nearly all available nutrients and out-competing native plants.

Parrots Feather

Parrot’s Feather (Myriophyllum aquaticum) is a native of lowland central South America that was first found in Britain in the 1960’s. It is now found in over 150 sites growing in ponds, reservoirs, streams and ditches, particularly where eutrophic conditions predominate.

Parrot’s feather forms dense growths blocking light from reaching submerged aquatic vegetation and removing oxygen from the water.