Japanese knotweed, or Polygonum cuspidatum is a large, herbaceous perennial, native to Japan. It has hollow, noded stems and can grow to about 3m high in each season. It belongs to the family Polygonaceae. Other botanic names for it include Fallopia japonica and Reynoutria japonica.
Its form gives it the appearance of bamboo, though it is not related to it. It is actually closely related to buckwheat, and yields a nice monofloral honey that is like a mild-flavored buckwheat honey, usually called "bamboo" honey by northeastern US beekeepers.
As an exotic, it is typically an invasive plant that is widely regarded as a weed. As an invasive plant, it is a colonizer of riparian ecosystems, roadsides and waste places. It can be found in 40 out 50 of the U.S states, and 6 Canadian provinces. It is a frequent invader in Europe and the U.K, where it has been illegal to spread Japanese knotweed in England since the 1980s. Native to Asia, Japanese knotweed was first introduced to Europe and the US in the 19th century.
Common English names for it include fleeceflower, huzhang, Hancock's curse, Japanese bamboo, and Mexican bamboo.
Closely related species include "Giant knotweed" (Polygonum sachalinense) and "Russian vine" (Polygonum aubertii).