Solidago canadensis L. as treated here is restricted to just two races native to the northeastern quarter of the U.S. and adjacent Canada. This follows Semple & Cook (2006 FNA). The species is distinguished by having upper stem leaves that are narrowly lanceolate, sparsely hairy on the veins and serrate on the margins. In the Maritimes, it can be confused with narrow-leaved forms of S. lepida. On the western and southern margins, var. hargeri can be confused for S. altissima; both have hairy lower stems. The species in the restricted sense includes only diploids.
The range is not fully resolved. The literature and data on the internet often do not make it clear which races of S. canadensis in the very broad sense are included in a dot distribution. A final distribution map can only be completed after examining a very large numbers of collections separated into S. altissima, S. canadensis (both varieties), and S. lepida. The map presented here is odd in having the westward extension in Missouri; these are var. hargeri collections, which may reach further west than the map indicates in Iowa and Minnesota. Most if not all of the more southern collections are var. hargeri. Plants identified as S. canadensis var. canadensis from northern Ontario, Québec, and Newfoundland have all been recently determined to belong in S. brendiae Semple (2013).
Two varieties are recognized in FNA (Semple & Cook 2006 FNA).
Statistical support for recognizing these varieties was recently presented in Semple et al. (2013) and Semple et al. (2015).