Cyanocorax sanblasianus nelsoni (Bangs and Penard) 1919; type locality Colima, Mexico. Occupies the bulk of the range of the species, from Nayarit south to northwestern Guerrero, Mexico.
Similar to nominate sanblasianus in plumage, but smaller (Hellmayr 1937) and brighter blue on the upperparts (Hellmayr 1937, Phillips 1986). The crest is more prominent in juveniles, and a remant of the crest is retained even in adults; in sanblasianus, the crest is lost in the year after hatching. Also differs in the iris color of the adult, and in the ontogeny of bill color; see Bare Parts.
Cyanocorax sanblasianus sanblasianus (Lafresnaye) 1842; type locality Acapulco. Distribution limited to the coast of central Guerrero.
Some earlier authors considered the Yucatan Jay Cyanocorax yucatanicus as a subspecies of sanblasianus, e.g. Blake and Vaurie (1962).
The San Blas Jay and closely related species - Bushy-crested Jay (Cyanocorax melanocyaneus), Yucatan Jay (Cyanocorax yucatanicus), and Purplish-backed Jay (Cyanocorax beecheii) - variously have considered to be members of the large genus Cyanocorax (Hardy 1969, Phillips 1986, American Ornithologists' Union 1998), or have been separated in the genus Cissilopha (Hellmayr 1934, Blake and Vaurie 1962).
Bonaccorso et al. (2010) constructed a phylogeny of Cyanocorax (sensu lato) New World jays based on a phylogenetic analysis of DNA sequence data from five genes, both mitochondrial and nuclear: NADH Dehydrogenase Subunit 2 (ND2; 1002 base pairs); cytochrome b (cyt b; 999 base pairs); the Adenylate Kinase gene, intron 5 (AK5); the ß-Fibrinogen intron 7 (ßfib7); and TGFß2.5. The "Cissilopha" species formed a monophlyetic clade, sister to the core species of Cyanocorax. The sister species to sanblasianus was beecheii; however, sanblasianus was paraphyletic with respect to beecheii. This paraphyly was an unexpected result, and "might indicate that speciation in this group occurred in a relatively short period of time, and not enough synapomorphies accumulated in the mitochondrial genes analyzed herein" (Bonaccorso et al. 2010: 904).