Japanese knotweed – Fallopia japonica - Plant & Pest Diagnostics

Japanese knotweed leaves with pink flowers

Japanese knotweed – Fallopia japonica

Fallopia japonica

Polygonaceae (Smartweed family)

MI Status

Non-native

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 a heart-shaped leaf base.

Japanese knotweed foliage with alternate heart shaped leaves. — Japanese knotweed leaves

Japanese knotweed flowers that are small, white to pink, and borne in elongated clusters. — Japanese knotweed flower

The photo shows the membranous sheath called an ocrea surrounds the stem at the base of each petiole. — New ocrea

Accessibility Questions:

For questions about accessibility and/or if you need additional accommodations for a specific document, please send an email to ANR Communications & Marketing at anrcommunications@anr.msu.edu.

Plant & Pest Diagnostics