(also known as cultivated knotweed, garden smartweed)
Polygonum polystachyum Wall. ex Meisn.
Aconogonum polystachyum (Wall. ex Meisn.) H. Haraldson
Persicaria wallichii Greuter & Burdet
- Moss, Flora of Alberta – No
-  Global Invasive Species Database –
-  NatureServe I-Rank – High/Medium
- AB Weed Act status – ?
"...has invaded riparian areas and other wetland places along the North and Central coast from Washington to California (also British Columbia). It also occurs in Massachusetts, but it is unclear if this species is spreading the eastern United States. This species reproduces vegetatively, fragmenting and resprouting easily. It also grows very quickly and outcompetes native plant species....."
 Link to Wikipedia, Polygonum polystachyum - "...native to Asia and it is planted as an ornamental. It has the capacity to become an invasive species. It is a rhizomatous perennial herb producing thick, hollow, erect stems easily exceeding one meter in length. Via its rhizomes it can form dense colonies..."
 Link to USDA Plants, Profile and map for Polygonum polystachyum Wall. ex Meisn., cultivated knotweed