Japanese knotweed

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For the Aphex Twin EP, see Donkey Rhubarb (EP).

iJapanese knotweed

Scientific classification

Kingdom:	Plantae
Division:	Magnoliophyta
Class:	Magnoliopsida
Order:	Caryophyllales
Family:	Polygonaceae
Genus:	Fallopia
Species:	F. japonica

Binomial name

Fallopia japonica
Houtt. (Ronse Decr.)

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 (Chinese: 虎杖; pinyin: Hǔzhàng), Hancock's curse, elephant ears, donkey rhubarb (although it is not a 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.

[edit] 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. Now, however, it is typically considered an invasive plant or weed where it has been introduced, and 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 a common invader in Europe, and in the U.K. it was made illegal to spread Japanese knotweed by the Wildlife and Countryside Act 1981.

Like other invasive herbaceous plants, such as Phragmites (Phragmites australis, giant reed), Japanese knotweed forms dense stands of stems that become impenetrable by other plants once well-established. The rapid growth of new shoots and leaves in the spring shades out any vegetation below, suppressing the growth of other plants, including established native species. The monocultures that often form following Japanese knotweed invasions contribute to reductions in native biodiversity.

[edit] 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, that is like a mild-flavored version of buckwheat honey (a related plant also in the Polygonaceae).

The young stems can be used as a spring vegetable similar to asparagus.

By semi-cultivating, for food, knotweed populations that invade sensitive wetland areas and drive out the native vegetation, this plant can be controlled very effectively, as shown in the pilot project of Bionic Knotweed Control in Wiesbaden, Germany. [1]

Both Japanese knotweed and giant knotweed are important concentrated sources of resveratrol, replacing grape byproducts. [2]

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."[3]