Closely related to and can hybridize with Japanese knotweed . Plants appear to have allelopathic properties. Introduced from mountains of Japan and Sakhalin Islands. Stalk bases fused and sheathing. Main stems erect, often arched near top, simple to minimally branched, grooved, thick, hollow , weakly woody, swollen at nodes, usually reddish-brown at maturity.
Twigs often zigzag slightly from node to node.
Tips acute to acuminate. Bases truncate to tapered. Stems sometimes pubescent, especially new growth. Leaves lanceolate , 10-20 cm long , often with short hairs on veins, margins, and lower surfaces. Bases slightly heart-shaped to tapered.