This genus formerly contained only the red-rumped bush tyrant. Molecular phylogenetic studies published in 2020 found that the red-rumped bush tyrant was a sister to the rufous-webbed bush tyrant in the monotypic genus Polioxolmis. The two species had diverged around 4.5 million years ago.[2][3] Based on these results, the genus Polioxolmis was merged into Cnemarchus placing both species in the genus Cnemarchus.[4][5]
The genus therefore contains the following two species:[5]
↑Chesser, R.T.; Harvey, M.H.; Brumfield, R.T.; Derryberry, E.P. (2020). "A revised classification of the Xolmiini (Aves: Tyrannidae: Fluvicolinae), including a new genus for Muscisaxicola fluviatilis". Proceedings of the Biological Society of Washington. 133 (1): 35–48. doi:10.2988/20-00005. S2CID229241271.