Japanese knotweed is not native to the UK, and was introduced around 1855 as a garden ornamental because of its exotic appearance. It is an herbaceous perennial, native to Japan and south-east Asia. The plant grows up to 3m tall and forms dense clumps. 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, 70mm - 50mm long. Flowers are creamy white, 3 mm wide, in dense clusters borne on the tips of stems. The underground rhizomes can be up to 10 cm in diameter, spreading 7m from the parent plant and up to a depth of 2m or more underground. Japanese knotweed seeds are not viable in the UK, however, hybrid crosses can produce viable seed. Japanese knotweed is most likley to spread as a result of disturbance.