The Black-throated Flowerpiercere is monotypic according to some sources (e.g., Clements et. al. 2015). However other sources (Graves 1980, Dickinson and Christidis 2014) divided the D. brunneiventris into two separate subspecies, Diglossa b. vuilleumieri and Diglossa b. brunneiventris. D. brunneiventris is found from the northern Peruvian low in Cajamarca, south of Cuzco (Graves 1982) to the west cordillera of the Andes until Tarapaca, Chile (Isler and Isler 1987). It occurs southward to the slope to La plaza, Bolivia east of La Paz (Graves 1982). Some of the main differences in the Peruvian population is the plumage of individuals, especially the extent of the gray flank to the underwing- coverts and the overall size of the malar stripe and supercilium (Graves 1982). D. b. vuileumieri is found in Antioquia, Colombia, to Paramillo, Colombia (Restall et. al. 2007). D. b. brunneiventris and D. b. vuilleumieri are so similar, that many are inseparable and the subspecies are mainly exist due to their geographic Isolation (Hilty 2011). However, the D. b. vuileumieri can be positive identify from the nominal population by having a smaller body and a larger black throat patch, with all the other features relatively constant (Graves 1982).
The Black Flowerpiercer (D. humeralis) belongs to the tanager family Thraupidae, within the diverse subfamily Diglossinae. This subfamily consists of 64 species mostly found at high elevations (Burns et al. 2014). There are 14 genera in this subfamily, including the Black Flowerpiercer's genus, Diglossa, which includes 18 species (Burns et al. 2014). Previous taxonomies have placed Diglossa in Coerebidae (honeycreepers), Parulidae (New World warblers), or Emberizidae (American Sparrows) (Burns et al. 2003). However, DNA analyses clearly indicate Diglossa flowerpierces are tanagers (Burns et al. 2014). Within tanagers, Catamenia is sister to the genus Diglossa (Burns et al. 2014). Vuilleumier (1969) subdivided this genus into four species-groups based on physical characteristics, and members of these groups also share habitat preference, social behavior, and feeding behavior (Isler and Isler 1987). The Black belongs to the lafresnayii species-group which also includes D. lafresnayii, D. gloriosissima, D. mystacalis, D. gloriosa, D. carbonaria, D. brunneiventris, and D. duidae (Vuilleumier 1969). Members of this group are aggressive towards other species and members of the same species (Isler and Isler 1987). Within the lafresnayii species-group, Vuilleumier (1969) recognized two superspecies, the lafresnayii superspecies and the carbonaria superspecies. Diglossa humeralis belongs to the carbonaria superspecies, along with D. carbonaria, D. gloriosa, and D. brunneiventris. D. humeralis, D. gloriosa, and D. brunneiventris have also been considered subspecies of D. carbonaria by some authorities (e.g., Storer 1970). Three of the remaining members of the lafresnayii species-group belong to the lafresnayii superspecies: D. lafresnayii, D. gloriosissima, and D. mystacalis. D. duidae was not assigned to a superspecies by Vuilleumier (1969). Two genetic studies have investigated relationships among flowerpiercers and included samples of D. carbonaria. Mauck and Burns (2009) sampled mtDNA data from all species of flowerpiercers. Burns et al. (2014) also sampled all species and included mtDNA data as well as some nuclear sequences from some species. Both studies found that the four members of the carbonaria superspecies form a monophyletic group. The amount of sequence divergence among the species within the carbonaria superspecies is much less than that found between most other avian species and is similar to the level seen within most species. However, the plumage patterns found within the carbonaria superspecies are the most variable of all flowerpiercer superspecies (Mauck and Burns 2009). Thus, the carbonaria superspecies represents a relatively recent radiation in which plumage has evolved rapidly. Phylogenetic analyses (Mauck and Burns 2009, Burns et al. 2014) disagree on the exact relationships of species within the carbonaria superspecies complex, with none of the trees showing strong support for relationships among species. Thus, relationships within the carbonaria superspecies remain to be resolved. Although the carbonaria superspecies is monophyletic, members of the carbonaria superspecies are not closely related to the lafresnayii superspecies or to D. duidae. Thus, Vuilleumier’s (1969) lafresnayii species-group is not monophyletic and should not be recognized.