Descriptions of major morphological features including those of the pollen, chromosome counts, and distribution data of the taxa of the family Urticaceae found in Canada are presented. There has been confusion in the species epithets applied to the genus Urtica. This study indicates that there are only three taxa in Canada: U. urens, 2n = 26; U. dioica ssp. dioica, 2n = 52; and U. dioica ssp. gracilis, 2n = 26 and 52. The tetraploid U. dioica ssp. gracilis ranges from the Rocky Mountains to the west coast while the diploid race occurs from the eastern side of the Rocky Mountains to the east coast. Artificial hybrids within the diploid race of Urtica dioica ssp. gracilis produced F1 plants with plenty of fertile seeds while a cross between a diploid and a tetraploid race of this taxon produced F1 plants with irregular chromosome pairing in the pollen mother cells and no seed set. The introduced U. dioica ssp. dioica ranges from Ontario to Newfoundland and the annual U. urens is widely scattered from the Yukon to Newfoundland. Laportea canadensis and Pilea pumila were found to have 26 somatic chromosomes; Boehmeria cylindrica, 28; and Parietaria pensylvanica, 16.