Fallopia japonica (Polygonum cuspidatum)

Japanese knotweed, also known as Japanese or Mexican bamboo, is a semi-woody, bushy perennial and a member of the Knotweed family. It is native to Japan and was introduced into the United States prior to 1890 as an ornamental. It also has been used for erosion control and landscape screening. By the early 1900's, it was established in the eastern United States and was reported naturalized in several areas near Philadelphia, Schenectady, and Atlantic Highlands, NJ. Its current distribution is Newfoundland westward to Ontario, Minnesota and Iowa, and southward into Tenneessee and North Carolina. Knotweed is found throughout North Carolina, but has been particularly aggressive in the mountains, where it has become one of the most troublesome perennial weeds. Japanese knotweed spreads rapidly from stout rhizomes and tolerates a wide variety of conditions including full shade, high temperatures, high salinity, and drought. Seeds are distributed by water in floodplains, transported with fill dirt, and to a lesser extent are wind-blown. It is found commonly near water sources, particularly riparian areas (river and stream bottoms), where it can survive severe floods and rapidly colonize scoured shorelines and islands. It also is a frequent inhabitant of disturbed sites, including waste disposal sites, rights-of-way, and abandoned homesites. Once established, knotweed is quite persistent and readily outcompetes existing vegetation by forming dense thickets under which nothing else can grow.

Japanese knotweed has stout, smooth, hollow, erect stems, swelling at the bases of the leaves, and grows up to 10 ft. tall. Fragments of stems which fall into the water or on damp soil may produce roots and establish new growth. Leaves are alternate, broadly oval to somewhat triangular, pointed at the tip, 2 to 6 in. long, and up to 5 in wide. The minute, greenish-white flowers are produced in axillary panicles in August through September. The seeds are mall, shiny, triangular, achenes. Plants survive until frost. The old stems eventually fall over during the winter. Rhizomes sprout in March to April.