Note the prominent, pinnately arranged secondary leaf veins. These features (among others) place this species in section Polygonum.
A key to all species of family Polygonaceae that are found in Alberta,
written by Lorna Allen and Linda Kershaw, is found here.
A key to Saskatchewan species of genus Polygonum, derived from the key in
the Flora of North America, is found here.
Polygonaceae: Answers to key questions in Budd's Flora leading to this family. The answers do not all apply to all genera in Polygonaceae, but they all do apply to genus Polygonum.