The genus contains eight living species, one of which (the loach minnow) is considered Vulnerable. It also includes the extinct Las Vegas dace, which was only first described in 1984 and had disappeared by 1986. The cheat minnow (Pararhinichthys bowersi), a natural hybrid of the longnose dace (R. cataractae) and the river chub (Nocomis micropogon), was formerly placed in this genus, but is now valid under Pararhinichthys.
The riffle daces are a basal lineage in an insufficiently resolved clade of American Leuciscinae. Such a group had been proposed on anatomical evidence, and was verified using mtDNA12S rRNAsequences.(Simons & Mayden 1997)
Simons, Andrew M. & Mayden, Richard L. (1997): Phylogenetic Relationships of the Creek Chubs and the Spine-Fins: an Enigmatic Group of North American Cyprinid Fishes (Actinopterygii: Cyprinidae). Cladistics13(3): 187–205. doi:10.1111/j.1096-0031.1997.tb00315.x (HTML abstract)
