U.S. Distribution: Areas of the northeast and northwest United States. Polygonum sachalinense, Fallopia sachalinensis) is a species of Fallopia native to northeastern Asia in northern Japan (Hokkaidō, Honshū) and the far east of Russia (Sakhalin and the southern Kurile Islands). University of Minnesota Extension discovers science-based solutions, delivers practical education, and engages Minnesotans to build a better future. Related species include giant knotweed (Reynoutria sachalinensis, syns. The stems are smooth, hollow and light green, resembling the canes of bamboo, and sparingly branched. While these plants can grow and exploit a range of site conditions, they seem most comfortable along riverbanks and roadsides here … Himalayan knotweed (figure 6) grows to 6 feet tall. The flowers are small, creamy white to greenish white, and grow in showy plume-like, branched clusters from leaf axils near the ends of the stems. It doesn’t reseed either. Giant knotweed is also considered invasive in Connecticut. Giant Knotweed is native to an island called Sakalin, off the coast of Japan, and, like its cousin, was brought to the British Isles to interest gardeners in the nineteenth century. Simple, alternate, toothless and heart shaped. Giant knotweed superficially resembles Japanese knotweed (Polygonum cuspidatum), and the two species hybridize. Bohemian knotweed (figures 4 and 5) is a hybrid of Japanese knotweed and giant knotweed and has characteristics of both parents. Persicaria polymorpha is a member of the knotweed family, but unlike that invasive thug Japanese knotweed it stays put and only increases its size where it’s planted. Flowers. Flowers on Giant knotweed have a green tint to their colour as opposed to the pure white of Japanese knotweed flowers. Angela Gupta, Extension educator; Amy Rager, Extension educator; Megan M. Weber, Extension educator. Due to their widespread use, the lack of natural predators, and their ability to spread by root and stem fragment… Japanese knotweed (left) and giant knotweed (right) occur throughout Pennsylvania. Each fruit contains a 3-sided achene that is small, shiny and brown. 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. Bohemian Knotweed (Fallopia bohemica) Naturally occurring hybrid between Japanese & giant knotweed Most common type of knotweed found so far Fruits are papery and broadly winged. This one features flowers that vary from light rose or dull pink to whitish-green. Large, light green and hollow with reddish joints. In Pennsylvania, seeds are mature in September . Giant knotweed has perfect flowers, including both female and male fertile flowers. Bohemian knotweed is a hybrid of giant knotweed and Japanese knotweed. 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