Japanese knotweed

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Japanese knotweed (Polygonum cuspidatum, syn. Fallopia japonica, 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" (Polygonum sachalinense) and "Russian vine" (Polygonum aubertii).

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 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.

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.

Other English names for Japanese knotweed include Fleeceflower, Huzhang (}; }), Hancock's curse, Donkey rhubarb (although it is not a rhubarb), Japanese bamboo, American bamboo, and Mexican bamboo (though it is not actaully a bamboo).

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

Both Japanese knotweed and Giant knotweed are sources of Resveratrol.

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