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Taxonomy

The species was first officially described by Swedish botanist Carl Linnaeus in 1758. Since then, numerous subspecies have been identified, but later classified as merely regional variants of the same species.

Using nuclear and mitochondrial DNA -sequence data to explore the phylogenic history of the green iguana, scientists from El Salvador, Mexico, and the United States studied animals collected from 17 countries. The topology of phylogeny indicated that the species originated in South America and eventually radiated through Central America and the Caribbean. The study revealed no unique mitochondrial DNA haplotypes for subspecific status, but did indicate the deep lineage divergence between Central and South American populations.

Naturalists once classified the Central American iguanas as a separate subspecies (I. i. rhinolopha), but this classification was later found to be invalid based on mitochondrial DNA, and iguanas with similar nose projections appeared randomly in other populations and interbred freely with those that do not share this trait. Genetic studies in the late 2010s still recovered I. rhinolopha as a distinct species, along with several other cryptic lineages present in I. iguana, and classifying only the South American populations may be the "true" green iguana. Two new insular subspecies (I. i. insularis and I. i. sanctaluciae) endemic to St. Lucia, Saint Vincent and the Grenadines and Grenada were also identified in 2019; a 2020 study also recovered both these subspecies as part of a distinct species, the southern Antillean horned iguana (I. insularis). The study also found the Saban black iguana (I. melanoderma), described in that study, to be the sister group of South American I. iguana, with the clade containing both being sister to that of I. insularis. The Reptile Database disagrees with these conclusions, and groups all of these within the green iguana, with four subspecies: I. i. melanoderma, I. i. insularis, I. i.sanctaluciae, and I. i. iguana.