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Invasive Species: Giant Knotweed

Invasive Species: Giant Knotweed

Giant Knotweed

Polygonum sachalinensis (Fallopia sachalinensis)

*Detected in Michigan*

Report this species:

Use the Midwest Invasive Species Information Network (MISIN) online reporting tool

- Or - download the MISIN smartphone app and report from your phone - MISIN.MSU.edu/tools/apps/#home

 

A branch of giant knotweed with long, green leaves and white flower spikes.

Photo courtesy of Leslie J. Mehrhoff, University of Connecticut, Bugwood.org.

Four people on a trail surrounded by giant knotweed shrubs.

Photo courtesy of Barbara Tokarska-Guzik, University of Silesia, Bugwood.org.

Identification:

  • Perennial, herbaceous shrub that can grow over 12 feet high.
  • Hollow stalks are light green, smooth and swollen at the nodes, resembling bamboo.
  • Similar to Japanese knotweed, and the two plants may hybridize.
  • Flowers are arranged in spikes near the end of the stem are small, numerous and greenish-white in color.
  • Flowers do not extend past the length of the leaves.
  • Flowers bloom in August and September in Michigan.
  • Giant knotweed leaves are 6-14 inches long, heart-shaped at the base and have fine hairs on the underside.

Habitat: Giant knotweed can be found in moist soils in sunny areas along roadsides, disturbed fields or vacant lots and along streams or river banks. 

Native Range: Japan.

U.S. Distribution: Areas of the northeast and northwest United States. Locations in Michigan’s Upper and Northern Lower peninsulas.

Local Concern: Giant knotweed spreads aggressively by roots (rhizomes) and cut or broken stems.  It can form dense thickets along streambanks, actually increasing erosion potential and decreasing habitat value.

MORE INFORMATION:

Giant Knotweed Invasive Species Alert - Printable PDF