I had trouble determining whether this specimen was P. aviculare or P. achoreum as it appears to have characteristics of both species, so this is a provisional identification.  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. herbs; NOT [shrubs or trees] land plants; NOT [water plants] plants not parasitic on trees plants with more than one pair of leaves; NOT [plants with a single pair of large reniform leaves] leaves alternate; NOT [leaves opposite] stipules present stipules forming a sheath above nodes flowers perfect