Giant Knotweed (Fallopia sachalinensis)

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Tall perennial that creeps via rhizomes. Stems erect, numerous, branched, 2-6 m tall, reddish, hollow. Basal leaves lacking; stem leaves alternate, 20-40 cm long, the blades widely egg-shaped, the bases heart-shaped, the tips gradually tapered, long stalked; stipules tubular, entire. Flowers in small axillary panicles; perianths 2-3 mm long, pale green or greenish-white, unequally 5-lobed, the outer lobes strongly winged.

Key Identifiers
  • Bamboo like stems
  • Leaves can reach 20-40 cm in length, with distinct heart shaped leaf base
  • Often forms extensive rhizomatous root system colonies
  • Hairs on the leaf undersides, especially along the midvein, are long and wavy in giant knotweed. These hairs are easiest to see with a hand lens during the spring and summer, often falling off later in the season. Flower clusters are generally shorter in length as the below leaf. Leaf and flower characters are most reliable when looking near the middle of a branch.

Tom Heutte, USDA Forest Service,

Tom Heutte, USDA Forest Service,
Location in Canada
BC, NB, Nfld, NS, Ontario, PEI and Quebec all report the presence of Giant Knotweed. Alberta is suspected to have a few ornamental locations of unconfirmed knotweed.

Resources Similar species
Japanese Knotweed (F. japonica) can be distinguished by the leaves, which are usually 3-10 cm, straight at the base, leaf tip abruptly pointed, leaf texture thick and leathery.

Hybrid Japanese Knotweed (F x bohemica) can be distinguished by the leaves, which are usually 5-30 cm, variable at the base, leaf tip variably pointed, leaf texture intermediate.

Elderberries (Sambucus spp.) have lance-shaped, pointed, and sharply toothed leaflets.

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For more information about the content of this document, contact Chris Neeser.
This document is maintained by Shelley Barkley.
This information published to the web on April 10, 2012.
Last Reviewed/Revised on August 21, 2018.