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Japanese Knotweed

Japanese Knotweed - Fallopia japonica


Japanese Knotweed - Fallopia japonica

Japanese knotweed (Fallopia japonica, syn. Polygonum cuspidatum, Reynoutria japonica) is a large, herbaceous perennial plant, native to eastern Asia in Japan, China and Korea. In the U.S.A. and Europe the species is very successful and has been classified as invasive in several countries.

A member of the family Polygonaceae, Japanese knotweed has hollow stems with distinct raised nodes that give it the appearance of bamboo, though it is not related. While stems may reach a maximum height of 34 m each growing season, it is typical to see much smaller plants in places where they sprout through cracks in the pavement or are repeatedly cut down. The leaves are broad oval with a truncated base, 714 cm long and 512 cm broad, with an entire margin. The flowers are small, creamy white, produced in erect racemes 615 cm long in late summer and early autumn.

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Closely related species include giant knotweed (Fallopia sachalinensis, syn. Polygonum sachalinense) and Russian vine (Fallopia baldschuanica, syn. Polygonum aubertii, Polygonum baldschuanicum).

Other English names for Japanese knotweed include fleeceflower, Huzhang , Hancock's curse, elephant ears, donkey rhubarb (although it is not a rhubarb), sally rhubarb, Japanese bamboo, American bamboo, and Mexican bamboo (though it is not a bamboo). In Japanese, the name is "itadori" (usually written in katakana). There are also regional names, and it is sometimes confused with sorrel.

Japanese Knotweed is a commercial source of resveratrol supplements. Huzhang root extract is a traditional Chinese medicinal treatment. It is also known as He Shou Wu, and the prepared herb is used as a blood tonic.

Cultivation and naturalisation

Japanese knotweed was first introduced to Europe and North America in the late 19th century for ornamental use, to prevent soil erosion, and as a forage crop for grazing animals.

Japanese Knotweed in Flower


Japanese Knotweed in Flower

Invasive species

In the U.S.A. and Europe Japanese knotweed is widely considered an invasive species or weed.[1] It is a frequent colonizer of temperate riparian ecosystems, roadsides and waste places. The success of the species has been partially attributed to its tolerance of a very wide range of soil types, pH and salinity.[2] Its rhizomes can survive temperatures of −35 C (−30 F) and can extend 7 metres (23 ft) horizontally and 3 metres (9.8 ft) deep, making removal by excavation difficult. The most effective method of control is by herbicide application close to the flowering stage in late summer or autumn.

It can be found in 39 of the 50 United States (PUSDA) and in six provinces in Canada. The species is also common in Europe. In the U.K. it was made illegal to spread Japanese knotweed by the Wildlife and Countryside Act 1981, and it is listed by the World Conservation Union as one of the world's 100 worst invasive species.[3] In the U.S.A. it is listed as an invasive weed in Ohio, Vermont, Virginia, New York and Washington states.[4]


Japanese knotweed flowers are valued by some beekeepers as an important source of nectar for honeybees, at a time of year when little else is flowering. Japanese knotweed yields a monofloral honey, usually called bamboo honey by northeastern U.S. beekeepers, like a mild-flavoured version of buckwheat honey (a related plant also in the Polygonaceae).

Japanese Knotweed Flower


Japanese Knotweed Flower

The young stems are edible as a spring vegetable, with a flavour similar to mild rhubarb. In some locations, semi-cultivating Japanese knotweed for food has been used as a means of controlling knotweed populations that invade sensitive wetland areas and drive out the native vegetation.[5]

Both Japanese knotweed and giant knotweed are important concentrated sources of resveratrol, replacing grape byproducts.[6] Many large supplement sources of resveratrol now use Japanese knotweed and use its scientific name in the supplement labels.[7] The plant is useful because of its year round growth and robustness in different climates.[8]

Japanese knotweed is a concentrated source of emodin, used as a nutritional supplement to regulate bowel motility. The roots of Polygonum cuspidatum are used in traditional Chinese and Japanese herbal medicines as a natural laxative. The active principle responsible for the laxative effect is emodin, present in its natural form as a complex of its analogs. Emodin has a mild laxative effect in doses of 20 to 50 mg per day.[9]

References and Notes

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