Japanese knotweed is a vigorous, clump-forming perennial, with tall, dense annual stems. Stem growth is renewed each year from creeping underground stems. It was introduced from Japan in 1825 as an ornamental plant.
Although it does not produce seeds, it can sprout from very small sections of rhizomes and, under the provisions made within the Wildlife and Countryside Act 1981, it is an offence to cause Japanese knotweed to grow in the wild. Much of its spread is likely to have been as a result of topsoil movement and construction traffic.