Based on a molecular phylogenetic study published in 2014 and a 2017 publication, the North American Classification Committee of the American Ornithological Society, the International Ornithological Committee (IOC), and the Clements taxonomy moved it to the resurrected genus Phaeoptila that had been introduced in 1861 by John Gould.

[5][6][7][4][8] However, as of 2020 BirdLife International's Handbook of the Birds of the World (HBW) retained it in Cynanthus.

It does not have an iridescent gorget like most other hummingbirds, but a deep gray throat with greenish flecks.

[9] The dusky hummingbird is found in southwestern Mexico from Michoacán and Morelos to Oaxaca.

The dusky hummingbird forages for nectar in the mid- to upper levels of trees.

[9] Dusky hummingbirds have been observered breeding in March, May, August, November, and December.

It makes "dry, slightly buzzy chips" and a chattering call that is described as similar to that of the broad-billed hummingbird (Cynanthus latirostris) but "softer and more liquid or spluttering".