Hamilton, C.W.; Reichard, S.H. (1992), „Current Practice in the Use of Subspecies, Variety, and Forma in the Classification of Wild Plants”, Taxon41 (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”, Taxon41 (3): 485–498, DOI:10.2307/1222819, JSTOR1222819