Japanese knotweed – Polygonum cuspidatum

Japanese knotweed foliage and flowers

Japanese knotweed foliage and flowers

Japanese knotweed flower

Japanese knotweed flower

New ocrea

New ocrea

Japanese knotweed

Polygonum cuspidatum Sieb. & Zucc
Polygonaceae (Smartweed family)

Life cycle
Aggressive, clump-forming perennial.

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

Stems
Stout, semiwoody, red to brown, hollow and bamboolike, 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.

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.

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.