Phytoplasmas are a diverse but phylogenetically coherent group of cell-wall-less bacteria affiliated with the class
Mollicutes
. Due to difficulties in establishing axenic culture, phytoplasmas were assigned to a provisional genus, ‘Candidatus Phytoplasma’, and the genus was embraced within the order
Acholeplasmatales
. However, phytoplasmas differ significantly from species of the genus
Acholeplasma
in their habitat specificities, modes of life, metabolic capabilities, genomic architectures, and phylogenetic positions. This communication describes the unique ecological, nutritional, biochemical, genomic and phylogenetic properties that distinguish phytoplasmas from species of the genus
Acholeplasma
and all other taxa in the class
Mollicutes
. Since such distinguishing properties of the phytoplasmas are not referable to the descriptions of the order
Acholeplasmatales
and of all other existing orders, namely
Mycoplasmatales
,
Entomoplasmatales
and
Anaeroplasmatales
, this communication raises the question of whether ‘
Candidatus Phytoplasma
’ should be retained in the order
Acholeplasmatales
or whether a novel provisional order and family should be created to accommodate the genus ‘
Ca. Phytoplasma
’.