Two subspecies are currently recognized (Clements et al. 2016):
cinereicauda, described as Oreopyra cinereicauda Lawrence 1867
Occurs in the highlands of Talamanca, Costa Rica (Stiles and Skutch 1989, Garrigues and Dean 2014).
Male is similar to nominate castaneoventris but the forecrown is bluer, the tail is grayish, and the breast is paler; females have grayish bronzy green central rectrices while the outer rectrices are slightly paler, the outer two or three pairs rectrices tipped pale gray; underparts are duller than in females castaneoventris (Wetmore 1968, Stiles 1999).
castaneoventris, described as Trochilus (---------?) castaneoventris Gould 1851.
Occurs in extreme western Panama (Ridgely and Gwynne 1989, Angehr and Dean 2010). See Detailed Description.
This species was described twice by Gould: Gould (1851) gave the name castaneoventris to a specimen in female plumage, and later (Gould 1860) described a specimen of a male as Oreopyra leucaspis). Bangs (1906) was the first to recognize that both names applied to the same species).
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. 2014). Lampornis belongs to the mountain-gem clade, and forms one of two major divisions within this clade; the other division includes the genera Lamprolaima, Eugenes, Panterpe, and Heliomaster (McGuire et al. 2014).
The genus Lampornis includes six other species: Green-throated Mountain-gem (L. viridipallens), Green- breasted Mountain-gem (L. sybillae), Amethyst-throated Hummingbird (L. amethystinus), Blue-throated Hummingbird (L. clemenciae), White-bellied Mountain-gem (L. hemileucus) and Purple-throated Mountain-gem (L. calolaemus). Lampornis castaneoventris is considered to be sister to L. calolaemus by most authors, and this has been confirmed by recent molecular phylogenies (García-Moreno et al. 2006, McGuire et al. 2014). The taxonomy of the castaneoventris/calolaemus group has been problematic. Briefly, within a small geographic area (Nicaragua to Panama), there are three phenotypic groups: birds with white throats and gray tails (cinereicauda); birds with purple throats and blue tails (pectoralis, calolaemus, and homogenes); and birds with white throats and blue tails (castaneoventris). These variably have been recognized as a single, highly variable species (e.g. Peters 1945, Wetmore 1967, Wetmore 1968, Stiles 1999), or as two species, one purple-throated (Purple-throated Mountain-gem Lampornis calolaemus) and one white-throated (White-throated Mountain-gem Lampornis castaneoventris, including cinereicauda) (e.g., American Ornithologists' Union 1983, 1998). Note that the distribution of Lampornis castaneoventris is geographically between that of the two western subspecies of Lampornis calolaemus (pectoralis, calolaemus) and that of the eastern subspecies (homogenes). Another alternative is to recognize castaneoventris (monotypic), cinereicauda, and calolaemus as separate species (Stiles and Skutch 1989, del Hoyo and Collar 2014). Hybridization is reported between these groups where the ranges abut, but the extent of hybridization is not clear. Bangs (1906) reported that among a large series (n = 63) of specimens of cinereicauda, half (33 specimens) had throats that were mixed blue and white, "in some [individuals] nearly half and half", suggesting a high level of hybridization. Other authors, however, report that specimens suggestive of hybridization are rather scarce (Black 1958, Slud 1964), and some reports of hybridization may be based on misinterpretations of the plumages of immature males (Stiles1999).