Japanese knotweed is not native to the UK, and was introduced around 1855 as a garden ornamental. It is an invasive and destructive herbaceous perennial, native to Japan and south-east Asia. Shoots emerge in spring and grow rapidly up to 3 m tall forming dense clumps that shade out native vegetation. It has fleshy green and red hollow stems with swollen red nodes, giving an appearance similar to bamboo. The leaves are green, triangular to heart-shaped, 70 – 150 mm long. Flowers appear from July to September and are creamy white, 3 mm wide, borne in dense clusters on the tips of stems. The underground rhizomes can be up to 10 cm in diameter, spreading 7 m from the parent plant and up to a depth of 2 m or more underground. Only female plants are present in the UK and they rarely set seed. Any seeds produced are likely to be from a cross with the closely related giant knotweed. The stems die back in winter, taking several years to decompose fully.
The plant favours areas such as roadsides, railway embankments, riverbanks and wasteland, and can be found throughout Norfolk.