Distribution
Japanese knotweed is native eastern China, Japan, and parts of Korea and Taiwan (Beerling et al. 1994). The variety of Japanese knotweed that has been introduced to the west, Fallopia japonica var. japonica, is native only to Japan (Shaw and Seiger 2002). Japanese knotweed was introduced to North America sometime before 1877. It is widely established in North America, from Newfoundland to Winnipeg and southern Manitoba, and the coastal region of British Columbia, and south as far as California, Louisiana and Georgia (Beerling et al. 1994; USDA-NRCS 2006). It is also established in Alaska (USDA-NRCS 2006).
Giant knotweed is native to northern Japan and Sakhalin Island (Ohwi 1965 in Conolly 1977). It has a North American distribution similar to Japanese knotweed, except that it is apparently still rare or absent from central North America (USDA-NRCS 2006).
In the Upper Great Lakes region, Japanese knotweed is established in Michigan, Minnesota, and Wisconsin, while giant knotweed is recorded from Wisconsin and Michigan (Voss 1985, WIS 2006, USDA-NRCS 2006). Hybrid knotweed has been recorded from Wisconsin and Minnesota (Schimpf and Pomroy 2005, WIS 2006), and almost certainly occurs in Michigan as well. [The USDA-NRCS (2006) map for giant knotweed in Minnesota shows known hybrid knotweed distribution; this population was originally misidentified as giant knotweed, which is not yet known from Minnesota (Schimpf and Pomroy 2005).]
| Japanese Knotweed | Giant Knotweed | Hybrid Knotweed |
|---|---|---|
| United States | United States | United States |
| Michigan | Michigan | Michigan |
| Minnesota | ||
| Wisconsin (WIS) | Wisconsin (WIS) | Wisconsin (WIS) |
| Wisconsin (UWSP) | Wisconsin (UWSP) | Wisconsin (UWSP) |
