In that essay, Bailey used only the rank of species for the cultigen, but it was obvious to him that many domesticated plants were more like botanical varieties than species, and that realization appears to have motivated the suggestion of the new category of cultivar.

The basic category of cultivated plants whose nomenclature is governed by this Code is the cultivar.A cultivar is an assemblage of plants that (a) has been selected for a particular character or combination of characters, (b) is distinct, uniform and stable in those characters, and (c) when propagated by appropriate means, retains those characters.

Cultivars may be selected because of a change in the ploidy level of a plant which may produce more desirable characteristics.