The genus was erected by
Nathaniel Lord Britton and
Joseph Nelson Rose in 1920, with the single species
Deamia testudo. The name honours Charles C. Deam, a plant collector who sent the plant to Britton and Rose. It was treated as a distinct monotypic genus until 1965, when
Franz Buxbaum merged it into
Selenicereus.
Alexander Doweld revived the genus in 2002, adding the species then treated as
Selenicereus chontalensis.
Molecular phylogenetic studies in 2017 (based on the two species then known) and in 2018 (three species) confirmed the
monophyly of the genus. It was placed in the tribe Echinocereeae, subtribe Pachycereinae. It was one of the early diverging members of the tribe in the
cladograms obtained in the 2018 study, with the species related as follows: }}
Species Two species were accepted in a 2017 study of the tribe
Hylocereeae which revived the genus
Deamia. A third species was described in 2018. A new species
Deamia funis was discovered in 2022 ,
Plants of the World Online still placed
D. chontalensis in the genus
Selenicereus. ==References==