Polygonum cespitosum or Tufted Knotweed is a summer annual weed plant of the family Polygonaceae, native to eastern Asia, from China to Japan and Southeast Asia, and introduced into North America. The plant grows to 3.5 feet (105 cm) in height with elliptic to lanceolate leaves, usually 20–75 mm (0.4-30.0 inches) long. It has small pink or red flowers arranged in tight terminal spikes.