Described as Trochilus (-----?) auriceps (Gould 1852); Gould gave the type locality as Mexico, but Moore (1938) reported that it was collected by Floresi, and "probably" is from Bolaño, Jalisco, Mexico.
This taxon was recognized as a monotypic species by Ridgway (1911) and Cory (1918), but Simon (1921) classified forficatus (Cozumel Emerald) as a subspecies of auriceps. Peters (1945) included all taxa of Chlorostilbon from Mexico south to northern South America, including auriceps, in a single species, Chlorostilbon canivetii (currently Canivet's Emerald; the highly polytypic species canivetii of Peters and other authors had the English name Fork-tailed Emerald). The classification of Peters was followed by many authors (e.g. Eisenmann 1955), and received some support from mention of specimens from south central Mexico (in the Districto Federal and Morelos) that were reported as intergrades between auriceps and nominate canivetii (Friedmann et al. 1950). Howell (1993) reviewed geographic variation in the four northernmost taxa of Chlorostilbon (auriceps, canivetii, forficatus, and salvini). Howell found no evidence that auriceps and canivetii are sympatric, much less of hybridization between the two, and further argued that all four taxa, all of which have allopatric distributions, each should be recognized as a distinct species. On the other hand, some authors recognize only a single species, Chlorostilbon mellisugus (Blue-tailed Emerald), for all taxa from Mexico south to Bolivia and central Brazil (Zimmer 1950, Schuchmann 1999).
Phylogenetic analysis of DNA sequence data reveals that hummingbirds (Trochilidae) constitute nine major clades, comprising the hermits, mangos, Patagona, topazes, coquettes, brilliants, mountain-gems, bees, and emeralds (McGuire et al. 2007, 2009). Chlorostilbon is the basal member of the emerald clade; other genera in this clade include Klais, Orthorhynchus, Campylopterus, Chalybura, Thalurania, Eupherusa, Microchera, Elvira, Aphantochroa, Taphrospilus, Amazilia, Chrysuronia, Hylocharis, Lepidopyga, and Damophila (McGuire et al. 2007, 2009).