Hamilton, C.W.; Reichard, S.H. (1992), "Current Practice in the Use of Subspecies, Variety, and Forma in the Classification of Wild Plants", Taxon, 41 (3): 485–498, doi:10.2307/1222819, JSTOR1222819
Hamilton, C.W.; Reichard, S.H. (1992), "Current Practice in the Use of Subspecies, Variety, and Forma in the Classification of Wild Plants", Taxon, 41 (3): 485–498, doi:10.2307/1222819, JSTOR1222819