Based on mtDNA, Lavin et al. (2018, Zoologica Scripta 47: 462–476) inferred 10 non-overlapping mitochondrial clades and six population clusters within E. coerulea and based on nuclear SNPs. Leaché et al. (2024, Journal of Heredity 115: 57–71) inferred 10 population clusters and nine multi-cluster clades that are only roughly consistent with subspecies proposed by Fitch (1938, American Midland Naturalist 20: 381–424). Neither set of authors proposed taxonomic changes, although Leaché et al. (op. cit.) performed analyses that failed to support more than one species within E. coerulea. We have re-circumscribed the subspecies to correspond to the three major clades within E. coerulea inferred by Leaché et al. (op. cit.) E. c. coerulea (synonym: E. c. principis) is applied to the clade of Pacific Northwest, Northern California, and Northern and Southern Coast Range clusters; E. c. palmeri is applied to the clade of Southern and two Central Sierra Nevada clusters; and E. c. shastensis is applied to the clade of Lower Cascades and two Northern Sierra Nevada clusters. The standard English names have been changed to reflect the geographic distributions of the taxa.

The results of Feldman and Spicer (2006, Molecular Ecology 15: 2201–2222), based on mtDNA, indicating that E. panamintina is derived from within E. multicarinata, was corroborated by Leavitt et al. (2017, Molecular Phylogenetics and Evolution 110: 104–121) using both mitochondrial and nuclear DNA sequences.

García-Vázquez et al. (2018, Journal of Biogeography 45: 1640–1652) and Blair et al. (2022, Biological Journal of the Linnean Society 135: 25–39) found deep divergences within G. infernalis in the United States and Mexico. Furthermore, samples of the newly described G. mccoyi (García-Vázquez, 2018, Herpetologica, 74: 269–278) from Coahuila, Mexico are nested within G. infernalis for both mtDNA and nuclear datasets.

Author citation corrected from Cope, 1880.

This species consists of two disjunct populations, one south of the Transverse Ranges in southern California and northern Baja California and one in the Tehachapi and Piute Mountains (Papenfuss and Parham, 2013, Breviora 536: 1–17), which is phylogenetically nested within the former (Parham and Papenfuss, 2009, Conservation Genetics 10: 169–176).

In the 8th edition of this list the names of subclades were indicated parenthetically, but Ctenocercus was omitted because it had not yet been proposed by Poe et al. (2017, Systematic Biology 66: 663–697).

Beckles (2020, Ph.D. dissertation. University of Miami, Coral Gables, Florida) found that some A. distichus mtDNA haplotypes from Florida are highly similar to Hispaniolan haplotypes, while others, although most similar to Bahamian haplotypes, are divergent from them. These findings suggest an older, possibly natural, colonization of Florida from the Bahamas, which bears on the potential natural occurrence of the species in Florida and the status of the proposed Florida subspecies (see de Queiroz et al., 2017, SSAR Herpetological Circular 43: 39), as well as a more recent introduction from Hispaniola.

The standard English name of this species has been changed to improve the information content of the name as well as to remove a potentially offensive eponym.

Richmond et al. (2017, Molecular Ecology 26: 3618–3635) corroborated the existence of two groups within this species found by Grimes et al. (2014, Southwestern Naturalist 59: 38–46) but did not infer restricted nuclear gene flow between those groups. They also presented genetic evidence corroborating previous hypotheses of hybridization with G. wislizenii (Montanucci, 1970, Copeia 1970: 104–123; 1978, Journal of Herpetology 12: 299–307).

See note on G. sila regarding hybridization between that species and G. wislizenii.

We have not recognized C. v. bogerti and C. v. utahensis, although Leavitt et al. (2020, Zoological Journal of the Linnean Society 190: 181–226) did not explicitly unite them with C. v. variegatus.

Douglas et al. (2010, Molecular Phylogenetics and Evolution 55: 153–167) stated that they found no mtDNA evidence to support the two subspecies of H. suspectum. Although they did not provide information on the collection localities of the sampled specimens needed to evaluate that conclusion, that information was provided subsequently by Schuett and Reiserer (2017, Herpetological Review 48: 798–801).

Valdivia-Carillo et al. (2017, Journal of Heredity 108: 640–649) presented evidence for three populations of Dipsosaurus dorsalis along the peninsula of Baja California, with gene flow between them. They did not include samples from the United States, mainland Mexico, or islands in the Gulf of California, nor did they propose any taxonomic changes.

Sumarli et al. (2024, Biological Journal of the Linnean Society 141: 572–588) presented results based on genomic RADseq data indicating that populations formerly included in S. ater from most of the Baja California peninsula are potentially a different species from those in the United States and Sonora (and northeastern Baja California), Mexico, although that finding does not affect the name of the species covered in this list.

Recent work by Mulcahy et al. (2022, PLoS One 17: e0264930) corroborates the findings of Blaine (2008, Ph.D. dissertation, Washington University, St. Louis, Missouri ) of substantial mtDNA sequence divergence between H. e. thermophila and H. e. elegans, although a large sampling gap remains, and that H. e. pulchra is not separate from H. e. thermophila, as proposed previously by Duellman (1955, Occasional Papers of the Museum of Zoology University of Michigan 569: 1–14).

Roelke et al. (2018, Journal of Natural History 52: 1017–1027) found that the two previously recognized subspecies of H. lacerata form reciprocally monophyletic mtDNA groups that correspond to differences in morphology and environmental niches and are separated by a presumed geographic barrier, leading those authors to propose that the two former subspecies be recognized as the species H. lacerata and H. subcaudalis. Those results were corroborated in a more detailed follow-up study by Hibbitts et al. (2019, Zootaxa 4619: 139–154). We have replaced the former standard English names “Northern Spot-tailed Earless Lizard” and “Southern Spot-tailed Earless Lizard” with the English names proposed by the latter authors.

Recent findings of Mulcahy et al. (2020, PLoS One 17: e0264930) corroborate Blaine’s (2008, Ph.D. dissertation, Washington University, St. Louis, Missouri) finding of three non-overlapping mtDNA haplotype clades, which correspond to the first three subspecies recognized here and in the 8th edition of this list except that H. m. ruthveni is nested within H. m. flavilenta.

See note on H. lacerata concerning the recognition and standard English name of this species. The authors cited in that note also found reciprocal monophyly in the mtDNA of northwestern and southeastern populations within H. subcaudalis but did not propose taxonomic recognition of those populations.

Gottscho (2015, Ph.D. dissertation, University of California at Riverside and San Diego State University), based on RADseq data, found that P. mearnsi samples were divided into northern and southern clades and populations, with P. slevini included within the southern population and sister to the remaining members of that population.

Leaché et al. (2017, Molecular Ecology 27: 2884–2895) noted that the populations within P. blainvillii corresponding to three mtDNA clades from their earlier study (Leaché et al., 2009, Proceedings of the National Academy of Sciences of the United States of America 106: 12418–12423) exhibit narrow geographic zones of admixture and were supported as species in some of their analyses (see also Yang and Rannala, 2014, Molecular Biology and Evolution 31: 3125–3135). Köhler (2021, Taxonomy 1: 83–115) recognized the two sets of populations corresponding to the earliest mtDNA divergence as subspecies, although he treated them as subspecies of P. coronatum (a name restricted to the populations from southern Baja California by Leaché et al., op. cit.). Because we are following Leaché et al. (op. cit.) in recognizing P. blainvillii and P. coronatum as separate species, we have treated the subspecies recognized and resurrected by Köhler (op. cit.) as a subspecies of P. blainvillii. The standard English name for the species has been returned to a commonly used, more biologically informative, and non-eponymous name.

Williams et al. (2019, PeerJ 7(e7746): 28) and Finger et al. (2022, Genome Biology and Evolution 14: evab260) found evidence from mtDNA, microsatellites, and genotyping-by-sequencing data for three primary and largely allopatric populations of Texas Horned Lizards in the Chihuahuan Desert, the Great Plains, and the southern Coastal Plain of the United States. Although they did not recognize these populations taxonomically, their demographic analyses indicate that the three populations are incompletely separated lineages. The earliest divergence is between the western (Chihuahuan Desert) and the two eastern populations. It corresponds to the divergence between the two primary mtDNA clades found by those authors and by Köhler (2021, Taxonomy 1: 83–115), who recognized them as subspecies.

Farleigh et al. (2021, Molecular Ecology 30: 4481–4496) presented evidence from phylogeographic analyses of nuclear SNP data that P. goodei, previously recognized based on mtDNA phylogeny (Mulcahy et al., 2006, Molecular Ecology 15: 1807–1826), is part of one of three genetic clusters within P. platyrhinos, although they did not propose taxonomic unification. Following Mulcahy et al. (op. cit.) and Sherbrooke (2020, Phrynosomatics 25: 1, 3–12), we have changed the standard English name of this species from “Goode’s Horned Lizard” used in the previous version of this list.

See note on P. ornatissimum for recognizing that taxon as a separate species from P. hernandesi. Leaché et al. (2021, Frontiers in Ecology and Evolution 9: 678110) inferred three main populations within P. hernandesi based on phylogenetic and demographic analyses of RADseq SNP data. Although they did not recognize those populations taxonomically, their analyses indicate that the three populations are incompletely separated lineages that experienced divergence with secondary contact. Those lineages largely correspond to the taxa Montanucci (2015, Zootaxa 4015: 1–177) recognized as P. brevirostris Girard, 1858 ≅ northern population, P. hernandesi ornatum Girard, 1858 ≅ western population, and P. hernandesi hernandesi Girard, 1858 plus P. bauri Montanucci, 2015 plus P. diminutum Montanucci, 2015 ≅ southern population. Hoza et al. (Ichthyology & Herpetology 111: 390–396) provided additional evidence that P. diminutum is not a separate species from P. hernandesi and is part of the southern population of that species.

Gottscho et al. (2024, Molecular Ecology 33: e17308) found subdivision of P. mcalli into genetic clusters on either side of the Colorado River as well as further subdivision of the northwestern cluster by the Salton Sea; however, they considered the differentiation of these clusters insufficient to warrant their recognition as species or subspecies.

Author citation updated from Girard, 1852.

Montanucci (2015, Zootaxa 4015: 1–177) proposed, based on morphological data, that populations of short-horned lizards from the arid short-grass plains of central and southern New Mexico represent a separate species from P. hernandesi, and that hypothesis was corroborated by the results of Leaché et al. (2021, Frontiers in Ecology and Evolution 9: 678110) based on principal component and phylogenetic analyses of RADseq nDNA data.

See note on P. goodei concerning the possibility that it is part of P. platyrhinos. Phylogenetic analysis of mtDNA sequences by Mulcahy et al. (2006, Molecular Ecology 15: 1807–1826; see also Jezkova et al., 2016, Ecography 38: 1–12) raised the possibility that lizards currently assigned to this species from the Yuma Proving Ground (southwestern AZ) represent a separate, unnamed species; however, that possibility is contradicted by the results of Farleigh et al. (2021, Molecular Ecology 30: 4481–4496).. The author citation has been updated from Girard, 1852.

Chan et al. (2020, PLoS ONE 15: e0238194) presented additional evidence (see Chan et al., 2009, Conservation Genetics 10: 131–142) for mtDNA and microsatellite differentiation among S. arenicolus populations. They found multiple nested genetic clusters with limited gene flow among them.

Wiens and Reeder (1997, Herpetological Monographs 11: 1–101) suggested that Sceloporus occidentalis becki should be recognized as a species based on diagnosability and allopatry relative to other populations of S. occidentalis. Salerno et al. (2023, Journal of Biogeography 50: 116–129) confirmed monophyly of island populations using mtDNA and suggested S. becki constitutes a species.

See note on S. magister. The standard English name has been changed from “Twin-spotted Spiny Lizard” to reflect the geographic distribution of the species.

Leaché et al. (2017, Molecular Ecology 26: 2306–2316) provided evidence for a 2 km northern shift in the hybrid zone of S. cowlesi and S. tristichus in Arizona over 10 years.

Wiens et al. (2019, Molecular Ecology 28: 2610–2624) found pronounced phylogeographic structure and relatively old divergences among S. jarrovii populations in the Madrean Sky Islands of southeastern Arizona. We reverted to the standard English name “Mountain Spiny Lizard” adopted in the 5th edition of this list (Crother et al., 2000, Herpetological Circular (29)), a name also used by McGinnis and Stebbins (2018, Peterson Field Guide to Western Reptiles and Amphibians, Houghton Mifflin Harcourt), and added “Madrean” to make it more specific.

Pavón-Vázquez et al. (2024, Systematic Biology 73: 323–342) inferred three lineages within the part of the Sceloporus magister complex that occurs north of Mexico: one in the Mojave Desert, Great Basin Desert, and Colorado Plateau, a second in the Sonoran Desert, and a third in the Chihuahuan Desert. Their results indicated both earlier divergence and less gene flow between the Chihuahuan Desert lineage and the other two lineages than between those two lineages. Although the authors treated all three lineages as a monotypic S. magister, their results would seem more accurately summarized by continuing (from the previous version of this list) to recognize the Chihuahuan Desert lineage as a separate species, S. bimaculosus, and the other two lineages (which were treated as separate species in the previous version of this list) as subspecies of S. magister. The standard English names of the subspecies have been changed to reflect the geographic distributions of the lineages.

Based on phylogenetic analysis of morphological and molecular (mt and nDNA sequence) data, Solis-Zurita et al. (2019, Zoologica Scripta 48: 419–439) found the taxon formerly designated S. variabilis marmoratus to be relatively distantly related to S. v. variabilis, which was inferred to be more closely related to other taxa then recognized as separate species. They, therefore, recognized both taxa (as well as the former S. v. olloporus) as species.

Given the small geographic distributions and close geographic proximity of the proposed subspecies, as well as the minor morphological differences and areas of intergradation between them (see Olson 1979, Catalogue of American Amphibians and Reptiles 227.1), those subspecies should be reevaluated with the addition of genetic data.

Bouzid et al. (2022, Molecular Ecology 31: 620–631) used RADseq data to characterize genetic structure and gene flow throughout the range of S. occidentalis. They found evidence for four or five populations inhabiting different geographic regions with admixture at the boundaries between them. They inferred long-term stability in the southern portions of the range and northward expansion followed by secondary contact in the north and suggested that S. occidentalis constitutes an ephemeral ring species. The authors did not address taxonomy, but their results indicate that the current subspecies taxonomy (e.g., Bell and Price, 1996, Catalogue of American Amphibians and Reptiles 631.1) needs revision. S. o. occidentalis corresponds approximately to the Pacific Northwest population. S. o. biseriatus and S. o. bocourti are part of a single population (central California west of the Sierra Nevada), for which the name S. o. biseriatus has priority. The former S. o. longipes is composed of an eastern Sierra Nevada population and a Great Basin population, which were sometimes inferred to form a single population and a separate Southern California population. We here treat the combined Great Basin and eastern Sierra Nevada population as one subspecies and the Southern California population as another; however, this creates nomenclatural complications because specimens from near the type locality of S. o. longipes are not assigned to any of these populations, and it is unclear if there are any available names for them (e.g., S. smaragdinus Cope, in Yarrow, 1875 is based on specimens from the Great Basin but is unavailable as a junior primary homonym of S. smaragdinus Bocourt, 1873 [Bell et al., 2003, Acta Zoológica Mexicana. 90: 103–174]; S. biseriatus nigroventris Bocourt, 1874 is based on one or more specimens from “Californie”, whose precise collection locality is currently unknown). The taxonomy of S. occidentalis needs further study.

See note under S. cowlesi.

DeRycke et al. (2020, Zootaxa 4778: 67–100), based on their own results and those of Gottscho et al. (2017, Molecular Phylogenetics and Evolution 106: 103–117), considered the species status of U. rufopunctata to be uncertain. The populations in question may be 1) part of U. notata, 2) part of U. cowlesi (endemic to Mexico), 3) a hybrid swarm between U. notata, U. cowlesi, and lizards from the geographic area between those species, or 4) a species that is incompletely separated from both U. notata and U. cowlesi.

After earlier studies (Trépanier and Murphy, 2001, Molecular Phylogenetics and Evolution 18: 327–334; Gottscho et al., 2017, Molecular Phylogenetics and Evolution 106: 103–117) suggested that populations of Fringe-toed Lizards from the Mohawk Dunes (Yuma Co., AZ) formerly considered part of U. rufopunctata constitute a separate species, DeRycke et al. (2020, Zootaxa 4778: 67–100) presented additional morphological and molecular data and results corroborating that inference and named the species.

Haenel (2017, Molecular Ecology 26: 606–623) documented introgression of U. ornatus mtDNA into some sympatric populations of U. graciosus.

Haenel (2007, Molecular Ecology 16: 4321–4334) found substantial phylogeographic structure in the mtDNA of U. ornatus, some of which is roughly consistent with previously recognized subspecies (U. o. ornatus, U. o. schmidti, U. o. wrighti), other of which is not (therefore, the remaining subspecies are designated legacy subspecies in the list below). The phylogeography of U. ornatus deserves further study, particularly regarding its taxonomic implications. See note under U. graciosus regarding introgression of U. ornatus mtDNA into U. graciosus.

The standard English name of this species is returned to that used in the 5th and 6th editions of this list (which used “Peninsular” rather than “Peninsula”).

“Madrean” was added to the standard English name of this species to make it more specific.

Richmond and Reeder (2002, Evolution 56: 1498–1513) presented mtDNA evidence that populations previously referred to P. gilberti represent three lineages that separately evolved large body size and the loss of stripes in late ontogenetic stages. Although they considered those three lineages to merit species recognition, they did not propose specific taxonomic changes. Subsequently, Richmond and Jockusch (2007, Proceeding of the Royal Society of London B 274: 1701–1708) and Richmond et al. (2011, American Naturalist 178: 320–332) have treated them as a single species based on extensive introgressive hybridization between two of the forms and the lack of prezygotic isolation between members of all pairs of them. The results of Richmond and Reeder (op. cit.) contradict the recognition of P. g. arizonensis, which is not differentiated from P. g. rubricaudatus and therefore has been eliminated from this list and indicate the existence of an unnamed and at least partially separate lineage within P. g. rubricaudatus (their clade C or Inyo clade). In addition, those results suggest that the former subspecies P. g. gilberti and P. g. placerensis form a single unit (their clade I or Sierran clade), while P. g. cancellosus and P. g. rubricaudatus also form a single unit (their clade A or southwestern clade), findings that are consistent with large areas of intergradation between the pairs of forms (e.g., Jones, 1985, Catalogue of American Amphibians and Reptiles. 372.1–3). We, therefore, recognize only three subspecies corresponding to the three lineages inferred by Richmond and Reeder (op. cit.).

Because the relationships within E. skiltonianus and between E. skiltonianus and the lineages within E. gilberti are complicated (Richmond and Reeder, 2002, Evolution 56: 1498–1513) and need to be analyzed using nuclear markers, we have retained the previously recognized subspecies as legacy taxa.

Jackson et al. (2017, Systematic Biology 66: 799–812) reanalyzed the nuclear sequence data from previous studies using phylogeographic models in the software PHRAPL and found support for three species with gene flow between central and eastern lineages along with relatively low levels of divergence. Leaché et al. (2019, Systematic Biology 68: 168–181) reanalyzed the same data using a hierarchical procedure based on heuristic genealogical divergence index (gdi) delimitation criteria with gdi values calculated from parameters estimated using the software BPP and found no support for multiple species.

Barley et al. (2021, American Naturalist, 198: 295–309) presented phylogenetic evidence that the populations of whiptails in the United States formerly referred to A. inornatus constitute a separate species, the oldest available name for which is A. arizonae. This taxon assumes the former standardized English name of “Aspidoscelis inornata” as the only populations formerly referred to that species that occur north of Mexico.

Both subspecies below were treated as species in the 8th edition of this list; however, Barley et al. (2021, American Naturalist, 198: 295–309) suggested that they are conspecific with A. burti (although A. b. xanthonotus was not sampled) based on phylogenetic and population structure analyses.

Based on phylogenetic analysis of two mtDNA gene fragments, Esquivel-Ramírez et al. (2021, Acta Zoologica 102: 129–142) inferred six evolutionary significant units (ESUs) within Mexican A. gularis, at least one of which (ESU 5) occurs in the United States. Although the ESUs were incongruent geographically with previously recognized subspecies, if treated as subspecies, ESU 5 would bear the name A. g. gularis. See note on A. scalaris regarding its treatment as a separate species from A. gularis. See note on A. laredoensis regarding hybridization between that species and A. gularis.

For the change in the ending of the species name, see note under Aspidoscelis.

See de Queiroz et al. (2017, SSAR Herpetological Circular 43: 41) regarding incomplete separation of this species from A. tigris. The subspecies A. m. marmoratus and A. m. reticuloriens are differentiated genetically but weakly so (Hall, 2016, Ph.D. dissertation, University of Texas at Arlington). For the change in the ending of the species name, see note under Aspidoscelis.

This newly named species was generated in the laboratory by hybridization between A. exsanguis and A. arizonae (as A. inornatus) (Cole et al., 2014, Brevoria (539): 1-20).

For the change in the ending of the species name, see note under Aspidoscelis.

For the change in the ending of the species name, see note under Aspidoscelis.

This newly named species was generated in the laboratory by hybridization between A. uniparens and A. arizonae (as A. inornatus) (Cole et al., 2017, Bulletin of the Museum of Comparative Zoology 161: 285–321).

Esquivel-Ramírez et al. (2021, Acta Zoologica 102: 129–142) found that A. scalaris and A.gularis form separate mtDNA clades, but they did not include samples from near the type locality of septemvittatus. Despite treating the two forms as conspecific, Hall (2016, Ph.D. dissertation, University of Texas at Arlington) found strong genetic differentiation in RADseq data between A. scalaris septemvittatus and A. gularis gularis.

For the change in the ending of the subspecies name, see note under Aspidoscelis.

Taylor et al. (2018, Herpetological Review 49: 636–653) proposed treating the previously recognized species A. flagellicaudus as conspecific with A. sonorae based on an analysis of new morphological data and a review of existing genetic data.

A. dixoni was removed from the 8th edition of this list based on the results of Cordes and Walker (2006, Copeia 2006: 14–26). Hall (2016, Ph.D, dissertation, University Texas at Arlington) corroborated their inference that A. dixoni and A. tesselatus resulted from a single hybridization event based on phylogenetic analysis of whole mt genomes and also found no evidence of differentiation between A. dixoni and A. tesselatus based on population structure analysis of RADseq data. For the change in the ending of the species name, see note under Aspidoscelis.

Incompletely separated from A. marmoratus. See de Queiroz et al. (2017, SSAR Herpetological Circular 43: 41) regarding the incomplete separation of this species from A. marmoratus. Mitochondrial clades inferred by Chafin et al. (2021, Frontiers of Biogeography 13.2, e49120) are largely congruent with the previously recognized subspecies A. t. mundus, A. t. punctilinealis, and A. t. septentrionalis, although A. t. punctilinealis would extend west of the Colorado River into southeastern California. A. t. tigris was sparsely sampled but may correspond to clade F, while A. t. stejnegeri was not sampled.

This newly named species was generated in the laboratory by hybridization between females of A. exsanguis and males of A. gularis and is not known to occur in the wild (Cole et al., 2023, Bulletin of the Museum of Comparative Zoology 163: 247–279).

Cole et al. (2017, Bulletin of the Museum of Comparative Zoology 161: 285–321) identified two putative natural hybrids between this species and A. arizonae (as Â. inornatus); the laboratory-generated species A. priscillae is a product of hybridization between members of the same two species.

Cole et al. (2019, American Museum Novitates. 3936: 1–8) studied karyotypes of Aspidoscelis from a population that had previously been treated as the species A. innotatus (e.g., Wright, 1993, in J. W. Wright and L. J. Vitt [Editors], Biology of Whiptail Lizards [Genus Cnemidophorus], Oklahoma Museum of Natural History, Pp. 27–81), which had been thought to differ from triploid A. velox in being diploid (Wright, op. cit.; see also Cuellar and Wright, 1992, Compte rendu des séances de la Société de biogéographie 68: 157–160). They found all individuals examined to be triploid and therefore treated this population as conspecific with A. velox.

The taxonomic distinction between populations of X. riversiana on San Nicolas Island (X. r. riversiana) and those on San Clemente and Santa Barbara Islands (X. r. reticulata) has been supported by analyses of both DNA sequences (Noonan et al., 2013, Molecular Phylogenetics and Evolution 69: 109–122) and morphology (Adams et al., 2018, Copeia 106: 550–562; Grismer et al., 2022, Vertebrate Zoology 7: 1–27).

See the note in the 8th edition of this list concerning the questionable status of this species