What: Japanese Knotweed (also known as Fallopia Japonica) is a large perennial plant.
Where: Knotweed is originally from Japan, China, Korea and other Eastern Asian countries.
Classification: Due to how successful knotweed has been in North America and Europe, the plant is now classified as an invasive species in many countries. It is listed as one of the world’s worst invasive species by the World Conservation Union.
Appearance: Japanese knotweed has thick hollow stems with a bumpy outer that look similar to bamboo. These stems can grow up to a maximum height of four metres, but most often knotweed is found in smaller clumps sprouting between cracks in the pavement. Japanese knotweed leaves are large and oval shaped with a shorter funnelled base. They are often between seven and fourteen centimetres long and five and twelve centimetres wide. Knotweed can flower and its blossoms are small and cream or white, and they tend to bloom in the late summer or early autumn.
Other names: Japanese knotweed is known under many names, including elephant’s ears, fleeceflower, donkey rhubarb (despite it not being a rhubarb), sally rhubarb, pea shooters, Hancock’s curse, Himalayan fleece vine, monkeyweed and monkey fungus.
Damage Caused: Due to the strong root system that knotweed has, and due to its speed of growth, knotweed can cause damage to many man-made structures such as roads, paving, flood defences, concrete foundations, retaining walls and architectural sites. There have also been cases where knotweed has reduced flood defences capacity to carry water.
Legislation: It is against the law to ‘plant or otherwise cause to grow in the wild’ under section 14(2) of the Wildlife and Countryside Act in the United Kingdom. It also has very strict disposal methods as it is classified under the Environmental Protection Act 1990 as ‘controlled waste.’ The Wildlife and Natural Environment Act 2011 came out in Scotland that superseded the Wildlife and Countryside Act 1981 and it stated that it is an offence to ‘intentionally or unintentionally spread Japanese knotweed.’
Natural Enemy: On the 9th March 2010 the decision was made to release a Japanese psyllid insect (Aphalara itadori) into the wild. The insect’s diets is very much specific to knotweed and it is hoped that it has the potential to control the growth of the plant.
Uses: Japanese knotweed can be used as a source of nectar for honeybees when the plant flowers. Many beekeepers use Japanese knotweed for this reason to create a monofloral honey usually known as bamboo honey. The stems of Japanese knotweed are edible and taste similar to rhubarb but with a more sour flavour. However, similar to rhubarb, Japanese knotweed contains an acid that when eaten too often can make conditions such as arthritis, kidney stones, hyperacidity, rheumatism and gout worsen.