Currently the taxonomic position of these forms is contested. The comprehensive taxonomic analysis in the Kew World Checklist of Selected Plant Families from 2002 considers all three forms to be distinct varieties of a single species. The Flora of North America publication considers the diploid form to be a distinct species, analyzing North American forms of the diploid variety, and does not analyse the morphology of Asian forms of the diploid variety. Also, in older literature, the name "Acorus americanus" may be used indiscriminately for all forms of "Acorus calamus" occurring in North America, irrespective of cytological diversity (i.e. both the diploid and triploid forms). The treatment in the Flora of China from 2010, which is followed in the Tropicos database system, considers all varieties to be synonyms of a single taxonomically undifferentiated species, pointing to morphological overlap in the characteristics singled out by Thompson.