Japanese knotweed, or Polygonum cuspidatum, is a large, herbaceous perennial plant, native to Asia (Japan, China and Korea).

A member of the Polygonaceae family, Japanese knotweed is also known by the botanical names Fallopia japonica and Reynoutria japonica. It 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.

Where it has been introduced, Japanese knotweed is typically considered an invasive plant or weed. It is a frequent colonizer of temperate riparian ecosystems, roadsides and waste places of America, and can now be found in 40 out 50 of the U.S. states, and 6 Canadian provinces. The monocultures that often form following Japanese knotweed invasions contribute to reductions in native biodiversity. The species is a frequent invader in Europe and the U.K., where it has been illegal to spread Japanese knotweed since 1981. It was first introduced to Europe and the U.S. in the late 19th century.

Japanese knotweed in Greeleyville, South Carolina

Japanese knotweed flowers in the late summer and early fall, producing many clusters of tiny, white flowers. Because of this, some beekeepers value the plant 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 plant also in the Polygonaceae family).

Other English names for Japanese knotweed include Fleeceflower, Huzhang, Hancock's curse, Japanese bamboo, and Mexican bamboo.

Closely related species include "Giant knotweed" (Polygonum sachalinense) and "Russian vine" (Polygonum aubertii).

Both Japanese knotweed and Giant knotweed are sources of Resveratrol.

External links

• Knotweed profile from invasivespecies.gov
• Japanese Knotweed (Polygonum cuspidatum) - A Noxious Weed in Washington
• Knotweed page on KnottyBits.com