Japanese knotweed Polygonum cuspidatum Sieb. & Zucc
Polygonaceae (Smartweed family)
Aggressive, clump-forming perennial.
Alternate, broadly egg-shaped, sometimes heart-shaped with a squared leaf base.
Stout, semiwoody, red to brown, hollow and bamboolike, often exceeding 6 to 8 feet in height. Stems are also jointed, forming a zigzag growth pattern.
A membranous sheath (ocrea) surrounds the stem at the base of each petiole. Reddish shoots arise from thick, sturdy and abundant rhizomes.
Flowers and fruit
Flowers are small, white to pink and borne in elongated clusters. The seed is enclosed in a single-seeded, shiny, dark brown to black, three-sided fruit.
Seeds and aggressive rhizomes.
(P. sachalinense F. W. Schmidt)
Differs by having a greater height and heart-shaped leaf base.