- Rheidae 2 species
- named after Rhea, wife of Saturn and mother of Zeus
- Rhea americana (Greater or Common Rhea)
- Pterocnemia pennata (Lesser or Darwins Rhea)
- named after Charles R. Darwin (1809-1882), the English zoologist and author of the theory of organic eveolution.
- pteron (Gr): feathers
- kneme (Gr): the leg between the knee and ankle or feather-legged
- pennatus (L): winged (they have small, useless wings for flight but can run very fast)