This order is represented by a single family restricted to Africa, Struthionidae (ostriches), with two species in a single genus, Struthio:
Traditionally regarded as a single species, Struthio camelus (Ostrich), mitochondrial DNA data seem to justify the distinction of two species,
Struthio camelus (Common Ostrich) and Struthio molybdophanes (Somali Ostrich). Common and Somali ostriches are thought to have been sparated by the formation
of the East African Rift Valley some 4 mya.
References
del Hoyo, J., N.J. Collar, D.A. Christie, A. Elliott, and L.D.C. Fishpool (2014), Illustrated Checklist of the Birds of the World, volume I
(Non-passerines), published by Lynx Edicions in association with BirdLife. (link)
Freitag, S. and T.J. Robinson (1993), Phylogeographic patterns in mitochondrial DNA of the Ostrich (Struthio camelus), The Auk 110 (3),
614-622. Doi:10.2307/4088425. (pdf)