Japanese knotweed

Polygonum cuspidatum Sieb. & Zucc

Life cycle

Aggressive, clump-forming perennial. 


Alternate, broadly egg-shaped, sometimes heart-shaped with a squared leaf base.


Stout, semi-woody, red to brown, hollow and bamboo-like, 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.

Japanese knotweed new ocrea
Japanese knotweed ocrea.

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.

Japanese knotweed foliage & flowers Japanese knotweed foliage Japanese knotweed flower
Japanese knotweed foliage and flowers. 


Seeds and aggressive rhizomes. 

Similar weeds

Giant knotweed (P. sachalinense F. W. Schmidt) Differs by having a greater height and heart-shaped leaf base.

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The MSU IPM Program maintains this site as an access point to pest management information at MSU. The IPM Program is administered within the Department of Entomology, fueled by research from the AgBioResearch, delivered to citizens through MSU Extension, and proud to be a part of Project GREEEN.