It formerly included additional species but following the publication of a molecular phylogenetic study in 2009 the genus was split into four separate genera.

The genus Anas was introduced by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae.

In 2009 a large molecular phylogenetic study was published that compared mitochondrial DNA sequences from ducks, geese and swans in the family Anatidae.

Their relationships are often undetermined: Several prehistoric waterfowl supposedly part of the Anas assemblage are nowadays not placed in this genus anymore, at least not with certainty: Highly problematic, albeit in a theoretical sense, is the placement of the moa-nalos.

[13] However, when compared to these species – which are representative of dabbling ducks in general – the moa-nalos are a radical departure from the Anseriforme bauplan.