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The History and Biology of Japanese Knotweed


By Unknown, E. Chargouey - Siebold collection at Naturalis, Public Domain,

People often ask who was to blame for introducing Japanese knotweed (Reynoutria japonica, formally Fallopia japonica) to the UK. His name was Philipp Franz Balthasar von Siebold (1796 – 1866), and he was a German physician who was working for the Dutch army when he was posted to Japan. Being a keen botanist, von Siebold collected as many native plants as he could during his time in Japan and brought them back to Europe with him.

Biology and Structural Damage

Knotweed typically grows in dense colonies (known as stands) which are all interlinked through the rhizome system. Stands can range in size from small areas of 1 square metre to very large stands, perhaps covering a hectare or more.


Japanese knotweed (Reynoutria japonica, formally Fallopia japonica) is common throughout the British Isles. While it often grows in damp conditions, it can be found on dry, droughty soils, in coastal marshland, railway ballast, derelict land and domestic gardens. It is probably true to say that if you are reading this in the British Isles there will be some knotweed within a couple of miles of where you are now ‐ and possibly nearer. Each season provides a specific means of identifying the plant.

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