Knotweed

Polygonum cuspidatum – Japanese knotweed

Polygonum sachalinense – Giant knotweed

Polygonum ×bohemicum – Bohemian knotweed

Keys to Identification

  • The leaves are alternate, can be large
  • Flowers are small, white, in 4 inch panicles

Family

Polygonaceae – Knotweed family

Other Names

Mexican bamboo

USDA Code

POCU6 – Japanese knotweed
POSA4 – Giant knotweed
POBO10 – Bohemian knotweed

Legal Status

Colorado Noxious Weed List A

Identification

Lifecycle

Perennial

Growth Form

Shrub

Flower

Flowers are greenish-white, ⅛ inch wide.  In upright panicles, 4 inches long

Flowers July-September

Seeds/Fruit

Fruit winged, 3-sided.  Seed black, shiny, about ⅛ inch long

Leaves

Leaves alternate, 3-11 inches wide and 5-15 inches long

Stems

Plants are up to 10 feet tall.  Stems hollow, reddish, rigid and jointed

Roots

Rhizomes to 18 feet long

Seedling

Seedlings emerge in April, but can sprout as late as July or August

Impacts

Ecological

Produces allelochemicals from the roots which inhibit the germination of surrounding plants.  Forms large thickets that displace native riparian plants

Habitat and Distribution

General Requirements

An escaped ornamental.  Found in riparian areas, gardens, disturbed sites and rights-of-way

Distribution

Has been found in Colorado in limited areas

Historical

Native to Asia

Biology/Ecology

Mode of reproduction

Reproduces by seed, rhizomes and vegetatively

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