Japanese Knotweed (Fallopia japonica, syn. Polygonum cuspidatum, Reynoutria japonica) is a large, herbaceous perennial plant, native to eastern Asia in Japan, China and Korea. In North America and Europe the species is very successful and has been classified as an invasive species in several countries.
Japanese knotweed is an upright, shrublike, herbaceous perennial that can grow to over 10 feet in height. As with all members of this family, the base of the stem above each joint is surrounded by a membranous sheath. Stems of Japanese knotweed are smooth, stout and swollen at joints where the leaf meets the stem. Although leaf size may vary, they are normally about 6 inches long by 3 to 4 inches wide, broadly oval to somewhat triangular and pointed at the tip. The minute greenish-white flowers occur in attractive, branched sprays in summer and are followed soon after by small winged fruits. Seeds are triangular, shiny, and very small, about 1/10 inch long.
Plant type | Herbs |
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Leaf structure | Simple |
Leaf margin | Entire |
Leaf arrangement | Alternate |
Management season | Early Spring to Late Summer |