- Contact information
For information on Lakes in Wisconsin, contact:
- Wisconsin DNR Lakes
Division of Water
Bureau of Water Quality
- Aquatic Invasive Species Contacts
Japanese knotweed (Fallopia japonica) - E. of S. Main St. and N. of Washington St.
- Date First Found
Japanese knotweed, in the buckwheat family, is a perennial that grows to heights of 5-10 feet in large clones up to several acres in size. The arching stems are hollow and bamboo-like, a reddish-brown to tan color;; they die, but remain upright through the winter. Mature leaves are 3-5 inches wide and 4-9 inches long, lighter on the lower surface, and egg to spade shaped;; young leaves are heart-shaped. Lacy 2 inch long clusters of tiny greenish-white flowers are produced in late summer and held upright at the leaf base. Japanese knotweed reproduces occasionally by seed, but spreads primarily by extensive networks of underground rhizomes, which can reach 6 feet deep, 60 feet long, and become strong enough to damage pavement and penetrate building foundations.