This infernal plant escaped from gardens in the early part of the nineteenth century and has been invading the countryside ever since. Listed as one of the worst invasive species in the world, it is an aggressive and widely naturalised alien, originating, as the name suggests, in Japan and South East Asia. In South and East Scotland it is widespread, but is more localised elsewhere including the Isles. It dies back after fruiting, but grows back rapidly in spring. According to reports it has been seen forcing its determined way through concrete, and is a hazard to road building and property development. The smallest piece of root can regrow vigorously, and strict guidelines must be followed in its removal from building sites.
It has wavy reddish green hollow stems which form dense clumps, and branch at the upper sections. The leaves are large, spade-shaped, almost triangular, ending in a point. Leaves are hairless and up to 15cm in length. Leaf stalks are long and red.
The dingy whitish flowers grow in drooping tassels from the leaf axils. Each flower has 5 tiny tepals and a white stalk. The knots in the leaf nodes are a feature of the plant and give rise to its name. In fact knotted leaf nodes are a frequent feature of all plants in the family Polygonaceae, to which this plant belongs.