Class Aves Linnaeus, 1758 - birds see Subclass Aves Linnaeus, 1758
   Subclass Neornithes Gadow, 1893 see Clade Neornithes Gadow, 1893
     Infraclass Eoaves Sibley et al., 1988 see Cohort Palaeognathae Pycraft, 1900
       Parvclass Ratitae (Merrem, 1813) see Subcohort Ratitae Merrem, 1813
         Order Struthioniformes Latham, 1790
           Suborder Struthioni
             Infraorder Rheides see Suborder Rheae Forbes, 1884
               Family Rheidae Bonaparte, 1849 - rheas
                 Genus Rhea Brisson, 1760
                   Rhea pennata d'Orbigny, 1834 - lesser rhea see Pterocnemia pennata (d'Orbigny, 1834)
                     Rhea pennata pennataᵀ d'Orbigny, 1834 - Darwin's rhea see Pterocnemia pennata pennata (d'Orbigny, 1834)