Types of Knotweed | Japanese Knotweed

Japanese knotweed is a rhizomatous perennial, currently classified as Fallopia japonica (and previously classified as Reynoutria japonica by Houttuyn in 1777 and polygonum cuspidatum by Siebold in 1846). It is a highly invasive plant that currently occupies most regions of the British Isles except Orkney. It is predominant throughout most of North America and is particularly abundant in the eastern United States. It has been observed as far north as Alaska and has colonised most of eastern Canada and British Columbia. It is also a cause for concern in several European countries, including France, Germany, Northern Italy, the Czech Republic and Norway, as well as increasingly being reported a nuisance weed in New Zealand and parts of Australia. Jim Knight, Parliamentary Under-Secretary for Rural Affairs, Landscape and Biodiversity, stated in a debate in the House of Commons on 11th October 2005 that removing Japanese knotweed from the UK using conventional methods would cost around £1.56 billion.

Japanese knotweed is native to Japan, Sakhalin Island, parts of China, the Kurile Islands, Korea, Vietnam and Taiwan and was widely distributed during the Nineteenth Century as an ornamental and fodder plant. It is an extremely hardy species, able to successfully colonise the inhospitable environment of bare volcanic gravel and lava fields. It can be found growing up to 2,400m – 2,600m high on Mount Fuji above the timber line. It is known by many names throughout the world, including crimson beauty, donkey rhubarb, Japan-pileurt, Asiatic knotweed, Japanese bamboo, Japanese fleece-flower, Pysen saethwr, elephant-ear bamboo, Kridlatka Japonska, Mexican bamboo, Rdest Sachalinski, Hu zhang, Renouée du Japan, Hancock’s curse and Sally rhubarb. (It is also known by those who have it growing on their land by other names far too colourful to print here.)

The common Japanese name for knotweed is ‘Itadori’, which simply means “strong plant” It is edible, with a taste reminiscent of rhubarb, and is a good source of Vitamin C. It can be used to make jam, fruit pies, soup, broth, ice cream or eaten stir-fried. Not all of the plant is suitable for consumption, though. For more information on this please see our Links page. Knotweed also has medicinal properties, as it contains relatively high levels of resveratrol. Accordingly it is used in the treatment of general allergy and inflammation complaints, including athlete’s foot, suppurative dermatitis, favus, herpes and gonorrhoea. Laboratory experiments on mice in Japan have produced promising indications that knotweed could also be suitable for the treatment of tumours and cancers. Most of the resveratrol currently sold commercially comes from either grapes or knotweed.

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