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Japanese knotweed

Common Name(s) Japanese knotweed, elephant ears, fleeceflower, Mexican bamboo, Japanese bamboo (although it is not a bamboo), donkey rhubarb (although it is not a rhubarb), huzhang

Scientific Name(s) Polygonum cuspidatum Siebold & Zucc. Synonyms: Fallopia japonica, Polygonum japonica and Renoutria japonica

Description

  • Semi-woody, herbaceous perennial
  • Grows in dense thickets up to 3m in height
  • Hollow, bamboo-like stems (although it is not a bamboo)
  • Stems are green to brownish-red in color often mottled with purple
  • Dark green leaves, 10-15 cm long
  • Leaves are broadly oval coming to a point at the tip
  • Flowers are clustered and green to white in color
  • Seeds are small (2-3mm) and winged

Habitat Japanese knotweed can grow in a variety of conditions which include drought, full shade, high temperatures and high salinity. The preferred habitat for Japanese knotweed is near water sources, and areas of low elevation. However, this plant can also be well established in waste sites and other disturbed habitats. This invasive plant can escape from private gardens, and can quickly become established in adjacent areas.

Invasion History Japanese knotweed was introduced into the United States some time in the late 19th century from its native range in eastern Asia. It was likely first introduced as an ornamental and for erosion control. Since then, Japanese knotweed has become an invasive species in 36 of the continental United States, and in many parts of Canada from coast to coast. Japanese knotweed spreads mostly by vegetative (clonal) means though networks of rhizomes. It can also be transferred via contaminated soil (seeds and rhizomes), by wind and water.

Regional Sightings Japanese knotweed can be found in many parts of Canada. It is found in southern British Columbia and provinces east of Ontario to Newfoundland. Here in Cape Breton, Japanese knotweed has increased its presence within Cape Breton Highlands National Park (CBHNP) during the last decade. In 2004, a study by Parks Canada indicated that Japanese knotweed was distributed in several sites within the Park between Pleasant Bay and Ingonish along the Cabot Trail highway. The study also indicated that knotweed might post a threat to native ecosystems and the ecological integrity of the Park. To read about the CBHNP management strategy, plase click here.

Potential Impacts Japanese knotweed easily crowds out native species and spreads rapidly. It can also survive and spread rapidly after large disturbances such as flooding. This invasive plant is so robust that it can penetrate and grow though asphalt. Once established, Japanese knotweed is very difficult to remove due to the depth and mass of its spreading rhizomes. Also, due to its rhizomes and small seed size if Japanese knotweed is removed and not disposed of properly it may lead to a larger outbreak of the species.

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