Native to Asia, and now found along the entire east coast of the United States, south through Florida and west to Louisiana.
A summer annual, growing either erect or sprawling, with many branches of thin, long stems. Reproduction is from seeds which germinate in the spring, with flowering from mid-summer into the fall. It is particularly a problem in moist situations, especially along borders of turf or ornamental plantings.
Mature plants may be several feet tall, or stems may be more sprawling and prostrate. The papery sheath, or ocrea, that is present around the base of the petiole and at stem junctions is indicative of this family of weeds. On tufted knotweed the ocrea has a distinct fringe of long hairs at the top margin, separating it from Pennsylvania smartweed.
Leaves are alternate and smooth except for sparse hairs along the veins. They are generally lanceolate and up to 6 inches long. Flowers range from bright pink to white, occurring in dense, spike-like clusters at the ends of the stems. Each individual flower is tiny.
Characteristicts Important to Control:
Very wet soils strongly encourage the growth of this plant, which can adapt to mowing with its prostrate growth potential.