Japanese Knotweed—Polygonum cuspidatum (Fallopia japonica)

Japanese knotweed is an invasive that grows quickly and aggressively, forming dense thickets. It thrives especially in riverbanks, roadsides and moist areas.

japanese knotweed along road
Dense thickets can clog small waterways and lower the quality of wetland habitats.

japanese knotweed plantLeaves are oval or heart–shaped with pointed tips, 6 inches long, 4 inches wide.

japanese knotweed flowers
Flowers are small and white and grow in showy lace-like branched clusters. Flowers appear in July and August.

japanese knotweed stem
Spreads aggressively, sprouting from rhizomes which can be 30 feet long.

japanese knotweed stem
Bamboo–like, hollow, reddish–brown stem that can grow 3 to 9 feet tall.

japanese knotweed flower
Each female flower can produce 1000 wing-like seeds.

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[Photos, left to right: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org; Richard Old, XID Services, Inc., Bugwood.org; James H. Miller, USDA Forest Service, Bugwood.org; Leslie J. Mehrhoff, University of Connecticut, Bugwood.org; Philip Rusted, Thurlow Countryside Management (r&d), Bugwood.org; Leslie J. Mehrhoff, University of Connecticut, Bugwood.org]