Amelanchier alnifolia var. pumila (Smooth Saskatoon, Dwarf Serviceberry) is reported as new to Canada from the Crowsnest Pass and Castle Mountain regions of the Rocky Mountains of southwestern Alberta. It occurs in open prairie habitat in cool montane parklands. Completely glabrous with prominently toothed leaves, and with a discrete distribution including the Rocky Mountains and adjacent plains, A. alnifolia var. pumila is a distinctive taxon worthy of recognition. At the Canadian sites it occurs with A. alnifolia var. alnifolia and a range of putative hybrids. The Canadian collections are described, and compare well with the type material. A key to the Amelanchier taxa of Alberta and British Columbia is included.