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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 -


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

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

Four people on a trail surrounded by giant knotweed shrubs.

Photo courtesy of Barbara Tokarska-Guzik, University of Silesia,


  • 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.


Giant Knotweed Invasive Species Alert - Printable PDF