Systematics

Monotypic.

Described as Chlorostilbon forficatus Ridgway 1885, with a type locality of Cozumel Island.

This taxon was recognized as a monotypic species by Ridgway (1911) and Cory (1918), but Simon (1921) classified forficatus as a subspecies of Chlorostilbon auriceps (Golden-crowned Emerald). Peters (1945) included all taxa of Chlorostilbon from Mexico south to northern South America, including forficatus, 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). Howell (1993) reviewed geographic variation in the four northernmost taxa of Chlorostilbon (auriceps, canivetii canivetii, canivetii salvini, and forficatus). Howell recommended that auriceps canivetii (and probably salvini) and forficatus each be recognized as 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).