Japanese, Giant, and Bohemian Knotweeds
(Polygonum cuspidatum, Polygonum cuspidatum, and Polygonum x bohemicum)
Japanese knotweed (Polygonum cuspidatum), Giant knotweed (P. cuspidatum), and their hybrid, Bohemian knotweed (P. x bohemicum) are bright green, bamboo-like, perennial plants that grow 5-16 feet tall and spread through lateral root systems (rhizomes). Stems are hollow between nodes, and often reddish-brown and swollen at the nodes. The base of the stem above each joint is surrounded by a membranous sheath. Leaves are alternate and large. Japanese knotweed leaves are broadly ovate or spade-shaped with low, bump-like scabers on the underside instead of hairs. Giant knotweed leaves are heart-shaped with long hairs underneath, and Bohemian plants typically have both leaf forms. The small, showy, greenish-white flowers develop on branched clusters and are present in late summer. Seeds are three-sided, black and shiny, and they develop in a papery-winged fruit.