Japanese Knotweed (Fallopia japonica)

 
 
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Description
Plant can reach up to 2-3 m tall, often forming dense thickets. Upright bamboo-like stems with long spikes of small white flowers very numerous along the branches. Leaves cut off square at broad base, continuing broad for most of their length and then curving in to pointed tip. Stems usually reddish and zig zag. Has a distinctive rhizome (root) system, which often extents to approximately 7 m horizontally from the parent plant and approximately 3 m vertically in depth below the parent plant.

Key Identifiers
  • Bamboo like stems
  • Often forms extensive rhizomatous root system colonies.
  • Leaves can reach 3-10 cm in length, with distinct straight leaf base
  • Leaves arranged in a zigzag pattern along the stem.
  • Distinctive orange centered rhizome (root).
  • Hairs on the leaf undersides especially along the midvein are reduced to barely noticeable bumps. 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 longer in length as the below leaf. Leaf and flower characters are most reliable when looking near the middle of a branch.
Location in Canada
BC, MB, Ontario, Quebec and eastern Canada all report the presence of Japanese Knotweed. Alberta is suspected to have a few ornamental locations of unconfirmed knotweed.

Resources

Richard Old, XID Services, Inc., Bugwood.org

Steve Manning, Invasive Plant Control, Bugwood.org

Similar species
Giant Knotweed (F. sachalinensis) can be distinguished by the leaves, which are usually 20-40 cm, deeply indented at the base, leaf tip pointed, leaf texture thin and flexible.

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 Nicole Kimmel.
This document is maintained by Shelley Barkley.
This information published to the web on April 10, 2012.
Last Reviewed/Revised on March 21, 2014.