There are three subspecies to Diglossa humeralis. Diglossa humeralis nocticolor inhabits the northern Colombian Santa Marta Mountains and Sierra de Perijá of Venezuela. D. h. noticolor is almost identical to the D. h. humeralis except that it lacks the gray shoulder patches. The body is all black with a bluish-gray tinted lower mandible. Diglossa h. humeralis can be found in the East Andes and the Páramo de Tamá of southwestern Venezuela. This subspecies sports the gray shoulders, gray crissum, and bluish-gray bill while the remainder of the body is black. Lastly, Diglossa h. aterrima can be found in western and central parts of the Andes Mountains from Colombia to Ecuador, as well as in Northwest Peru. Unlike the other subspecies, aterrima does not have the bluish-gray lower mandible, it has an all black bill to go along with its all black body. (distribution information from Clements 2015; plumage descriptions from 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.