Japanese knotweed


 * Donkey Rhubarb redirects here. For the EP by electronic music artist Aphex Twin, see Donkey Rhubarb

Japanese knotweed (Fallopia japonica, syn. Polygonum cuspidatum, Reynoutria japonica) is a large, herbaceous perennial plant, native to eastern Asia in Japan, China and Korea.

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 3–4 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, 7–14 cm long and 5–12 cm broad, with an entire margin. The flowers are small, creamy white, produced in erect racemes 6–15 cm long in late summer and early autumn.

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 actually a bamboo).

In Japanese, the name is "itadori" (usually written in katakana). There are also regional names, and it is sometimes confused with sorrel.

Cultivation and naturalisation
Japanese knotweed was first introduced to Europe and North America in the late 19th century for ornamental use, for planting to prevent soil erosion, and sometimes as a forage crop for grazing animals. It is sometimes considered an invasive species or weed. It is a frequent colonizer of temperate riparian ecosystems, roadsides and waste places. 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 is listed by the World Conservation Union as one of the world's 100 worst invasive species.

Uses
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 nice monofloral honey, usually called "bamboo" honey by northeastern U.S. beekeepers like a mild-flavored version of buckwheat honey (a related plant also in the Polygonaceae).

The young stems are edible as a spring vegetable, with a flavor 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.

Both Japanese knotweed and giant knotweed are important concentrated sources of resveratrol, replacing grape byproducts. Many large supplement sources of Resveratrol now use Japanese knotweed and use its scientific name in the supplement labels. Japanese knotweed is being harvested because of its year round growth, and robustness in different climates, although it is still considered a troublesome weed.

Japanese knotweed is a concentrated source of emodin, used as a nutritional supplement to regulate bowel motility. "Extract from the roots of Polygonum cuspidatum is 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. It has been reported that emodin has a mild laxative effect in doses of 20 to 50 mg per day."