Japanese Knotweed

Now very widespread in Great Britain, Japanese knotweed is highly abundant in urban areas particularly in parts of South Wales. Generally less abundant in rural areas. The species was first introduced to Europe in 1849 and was recorded in South Wales in 1886 as an ornamental, architectural plant. The species is still widely grown in parks and gardens. 

This invasive plant species spreads rapidly, forming tall, dense, annual stems and often grows into dense thickets. Stem growth is renewed each year from the deeply penetrating rhizomes (creeping underground stems). In spring, reddish-purple fleshy shoots emerge from pink buds at ground level. They grow rapidly and in summer they produce dense stands of tall bamboo-like canes. These have characteristic purple flecks and produce branches from nodes along its length. Leaves are heart or shovel-shaped. The stems die back to ground level in winter, but the dry canes remain for several months. They produce creamy-white flowers in late summer to early autumn. In Great Britain, plants are male-sterile clones, producing no seeds. However, plants are capable of hybridising with  Fallopia species.

Dispersal is often as a result of human activity (either deliberate or inadvertently). If plant or sections of root are discarded, these can establish easily in new locations and is a particular problem along riverbanks where excavated plant fragments may travel downstream.

Environmental impact is somewhat unknown as it usually occurs in urban areas where native flora is already negatively impacted. Alterations in habitat and biological communities caused by Japanese knotweed are known to impact salmonid fisheries and there is concerns that the species will impact conversation and management of UK waterways.

• To find out more information about removing Japanese knotweed from land or ways of controlling it please see the government website: Japanese Knotweed Guidance.
• Sample types include: leaves, stems, flowers and roots.
• It is important that samples are fresh due to fungal pathogens which may grow on dead plant material and be amplified during the PCR process. Therefore, please send samples to us as soon as possible, or freeze them immediately if you are intending to send samples in as a batch.
• *Sampling can be conducted using a biological collection kit or samples can be sent in in a sealed envelope/parcel without the use of a kit.*