Japanese knotweed
August 27, 2015
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EmailPolygonum cuspidatum Sieb. & Zucc
Life cycle
Aggressive, clump-forming perennial.
Leaves
Alternate, broadly egg-shaped, sometimes heart-shaped with a squared leaf base.
Stems
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 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 and flowers.
Reproduction
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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