United States
Department of Agriculture

Forest Service

Northeastern Area

Japanese Knotweed — Polygonum cuspidatum Sieb. & Zucc.

Japanese knotweed is native to Eastern Asia, and is one of the first plants to appear on volcano slopes after volcanic activity. It was introduced to the United Kingdom as an ornamental in 1825, and from there to North America in the 19th Century.

It appears to require high-light habitats, and does very well along roadways and rivers. It reproduces by seed and large rhizomes, which may reach a length of 40 to 60 feet. A small piece of rhizome can float down a river and begin to grow once it is deposited on land. These buried rhizomes have grown through 2 inches of asphalt!

Native range: Japan and Eastern Asia

For more information visit: http://www.nps.gov/htdocs2/plants/alien/map/pocu1.htm

Japanese knotweed is also known as Japanese or Mexican bamboo, because the stem becomes woody and has enlarged nodes similar to those of a bamboo fishing pole.

It is a very fast grower that can reach a height of 10 feet and overtop native vegetation very quickly.

Individual Japanese knotweed

The heart-shaped leaves are arranged alternately along the stem. Although variable in size, the leaves are normally about 6 inches long by 3 to 4 inches wide. Minute greenish- white flowers are produced in axillary panicles.

This plant is a threat to native vegetation because it often forms dense patches, which shade out all other plants. It is a particular threat in riparian areas where it can survive floods and quickly colonize scoured streambanks. Japanese knotweed is difficult to eradicate once it has become established.


Alternating heart-shaped leaves with sprays of minute flowers arising in the angle between the leaf and the stout stem.


Dense patch of Japanese knotweed  


Photographs by Rosemarie Boyle.

For additional information, contact:

USDA Forest Service
Wayne National Forest
Rosemarie Boyle
219 Columbus Road
Athens, OH 45701
(740) 592-0200
USDA Forest Service
Forest Health Protection
180 Canfield Street
Morgantown, WV 26505
(304) 285-1541


July 1999