Reynoutria japonica Houtt.

Japanese Knotweed; Japanese Bamboo; Japanese Buckwheat

Herb

Perennial

Vascular

Japanese Knotweed is an introduced herbaceous perennial in the Buckwheat family (Polygonaceae). It is native to China, Japan, Korea, Taiwan, and Russia. In Alabama it has been collected from scattered areas across the state. Japanese Knotweed occurs on roadsides and railroad margins, along ditches and streams, in the margins of fields and pastures, on urban lots, and in other disturbed areas. It is a perennial from thick rhizomes. Stems are erect, 3-6 feet in height, usually branched above the middle, striate, papillate, and often red spotted. Leaves are alternate, deciduous, petiolate, ovate to elliptic in outline, glabrous, and with entire margins. Flowers are produced in axillary panicles. Flowers are either bisexual or unisexual (pistillate). The perianth is white or greenish, campanulate, glabrous, with 5 petal-like tepals and 6-8 stamens. The three outer tepals are larger and winged. The fruit is an achene. Japanese Knotweed was introduced as an ornamental in the 1860’s. It is an aggressive weed, forming extensive colonies that exclude native vegetation. It has also been planted as a nectar source for bees and to reclaim strip mined sites. Once established it is difficult to eradicate. It is listed as a noxious weed in Alabama, California, Oregon, Vermont, and Washington.—A. Diamond.

**

Not Native

**