Photo: Japanese Knotweed Cluster (©Frank Vincentz (Own work) [GFDL]
Japanese Knotweed (Fallopia japonica) is a non-native invasive plant originating from Japan, Taiwan and Northern China. Bought over here in the 19th century, the plant was grown and sold as an ornamental plant. Japanese Knotweed is a tall herbaceous perennial plant, which forms dense bamboo like thickets. This species is widespread across the UK, with noticeable infestations.
Able to survive naturally within the UK, Japanese Knotweed has unfortunately become a common sight across much of the UK, even colonizing alongside our waterways. Japanese Knotweed can grow in dense thickets which can outcompete and shade out native species, reducing biodiversity.
Japanese Knotweed contributes to bankside erosion as well as increase the likelihood of flooding. The plant is able to find weak spots in man-made materials such as cracks and defects and can often be seen growing through asphalt, patios, landscaped areas and even concrete. This can pose a threat to buildings, structures and our waterways, potentially degrading locks, walls and banks, affecting integrity of a waterway.
Despite only being able to spread through vegetative means in the UK, all it takes are a few fragments from the stem or rhizome to sprout in a new area, making it extremely difficult to effectively control the spread of this plant. Japanese Knotweed grows particularly well on disturbed areas of land which can include urban areas, waste sites, road sites, railways and riverbanks.
You should record the presence of invasive species on a national database. You can record online at the Non-native Species Secretariat website. You should also alert the appropriate land owner, council and or management body to the presence and location of this plant.