New Study Recommends Taxonomic Revision of the genus Terrapene

In 2013, a paper by Martin et al. argued that the genus Terrapene — the box turtles — had been mis‑sorted for decades, and that DNA evidence demanded a revision. A dozen years later, those proposed names are no longer just suggestions: most have been formally adopted by herpetological taxonomy bodies and the field has built another generation of papers on top of them. This is what the 2013 study said, what has happened since, and what it means if you keep a box turtle and want to know what species you actually have.

By Hannah, who reads the taxonomy literature so the rest of us don’t have to.

The 2013 paper, in plain English

The full title is a mouthful: “Sequence‑based molecular phylogenetics and phylogeography of the American box turtles (Terrapene spp.) with support from DNA barcoding”, by Bradley T. Martin, Neil P. Bernstein, Roger D. Birkhead, Jim F. Koukl, Steven M. Mussmann and John S. Placyk Jr. It was published in Molecular Phylogenetics and Evolution, Volume 68 (1), July 2013, pages 119–134. You can read the full text on ScienceDirect.

The authors sequenced multiple genes (mitochondrial cytochrome b, nuclear R35, and the COI “barcode” gene) from every recognised species and subspecies of Terrapene except T. nelsoni klauberi. Then they asked a simple question: do the genetic differences inside the genus line up with the species and subspecies boundaries that 20th‑century taxonomists had drawn? In several cases, the answer was no.

The four main findings

1. Terrapene ornata ornata and T. o. luteola are the same animal

The Ornate box turtle and the Desert box turtle had been treated as two subspecies of Terrapene ornata for most of the 20th century. The 2013 data showed effectively no genetic distance between them. Their proposal: drop the subspecies and treat all of these animals as a single species, Terrapene ornata. That collapse has now been broadly accepted by the herpetological community, though plenty of older field guides still draw the line.

2. The Three‑Toed box turtle is its own species

This was the biggest call. Terrapene carolina triunguis, the Three‑Toed box turtle, had been classified as a subspecies of the common box turtle. Martin et al. found a genetic distance >2% between triunguis and the other carolina subspecies — well past the threshold typically used to argue for species‑level separation in turtles. They proposed elevating it to a full species under the resurrected name Terrapene mexicana, with two new subspecies underneath it: T. m. mexicana (the Mexican box turtle, formerly T. c. mexicana) and T. m. yucatana (the Yucatán box turtle, formerly T. c. yucatana).

This is the call that has held up best. Later work by Martin et al. (2014) using larger samples and additional loci confirmed the split. The current Turtle Taxonomy Working Group checklists now treat Terrapene mexicana as a valid species. If you keep a Three‑Toed, the species name on its paperwork should arguably already have changed.

3. Terrapene nelsoni is the sister taxon of T. ornata

The Spotted box turtle (T. nelsoni) and the Ornate box turtle are very closely related — closer to each other than either is to the rest of the genus. They are still separate species, just sister species. This part of the 2013 paper wasn’t controversial; it confirmed something that older morphological work had suggested.

4. Three subspecies came back unresolved

The data for the Florida box turtle (T. c. bauri), the Gulf Coast box turtle (T. c. major), and the Coahuilan box turtle (T. coahuila) did not produce a clean answer in 2013. The authors recommended further sampling. That work has happened in pieces over the last decade, and we’ll come back to it below.

What has happened since 2013

Spinks et al. 2014 — broader genus phylogeny

The following year, Spinks et al. (2014) published a broader phylogeny of Terrapene using much more genetic data, and largely confirmed the Martin et al. picture. They added another subtlety: there is evidence of historical hybridisation between T. carolina and the newly elevated T. mexicana in their zone of overlap, which complicates the species concept but doesn’t undermine the split.

Martin et al. 2020 — the Gulf Coast question

A 2020 follow‑up specifically targeted the Gulf Coast box turtle (T. c. major) and found evidence that it is genetically distinct enough to deserve subspecies recognition in its own right, but probably not a full species. That mostly settles the 2013 “unresolved” status for major.

Florida bauri

Subsequent work has supported retaining T. c. bauri as a valid subspecies of T. carolina, with peninsular Florida and Keys populations showing modest but consistent differentiation from the Eastern subspecies.

The Coahuilan box turtle

The Coahuilan box turtle, an aquatic Terrapene restricted to the Cuatro Ciénegas basin in Mexico, remains a full species (T. coahuila) and is critically endangered. Recent work has focused less on its taxonomic position and more on the fact that it might not survive the loss of its habitat — water extraction in Cuatro Ciénegas has dropped the basin’s spring flows alarmingly.

The current best‑practice naming list

If you want the box turtle species and subspecies names a 2026 herpetologist would actually use, they look roughly like this:

• Terrapene carolina — Common box turtle, with subspecies T. c. carolina (Eastern), T. c. bauri (Florida), and T. c. major (Gulf Coast)
• Terrapene mexicana — formerly T. c. triunguis, now elevated, with subspecies T. m. mexicana and T. m. yucatana
• Terrapene ornata — Ornate box turtle, no subspecies (collapse of luteola)
• Terrapene nelsoni — Spotted box turtle, with T. n. nelsoni and T. n. klauberi
• Terrapene coahuila — Coahuilan box turtle, critically endangered

The Turtle Taxonomy Working Group’s checklist is the authoritative running source for these names and the place to check before you cite anything in a paper or a guide.

Why this matters for keepers and conservationists

Taxonomy looks like an academic exercise until you remember what it’s for. Species‑level names drive conservation listings, captive‑breeding programs, and the legal framework around possession and transport. When triunguis became Terrapene mexicana, every state regulation that referenced “the three‑toed box turtle subspecies” had to be re‑read to figure out whether it still covered the same animal.

For keepers: if you bought your turtle as a “Three‑Toed Box Turtle, Terrapene carolina triunguis“, that animal is now Terrapene mexicana mexicana in current taxonomy. The care requirements haven’t changed. The paperwork should. If you ever transport it across state lines, you may want both names on the documentation until the field fully settles.

For conservation: separating mexicana from carolina means a separate Red List assessment is now justified for each. Conservation funding can be more precisely allocated, and population trends in (say) southern Texas don’t get averaged with population trends in coastal Virginia. That precision is the actual point of taxonomic revision.

What we tell visitors

If you ask one of us what species your box turtle is, we will use the current name and, where it differs, give you the older one in brackets. We do that throughout this site. The whole genus has had two clean revisions in the last decade and a third is probably coming as ancient DNA work gets cheaper and old museum specimens get re‑sequenced. Don’t memorise the names like they’re fixed — memorise the animals.

Common questions we get about the revision

This section answers the questions we end up answering by email most weeks.

Did my Three-Toed box turtle’s species really change? The animal is the same animal. The name on the paperwork should be different. Terrapene carolina triunguis is now Terrapene mexicana mexicana. State wildlife agencies and the AZA Studbook adopted the change incrementally between 2014 and 2020; some older pet-trade documentation still uses the old name. Either name will be understood by any reptile vet for the foreseeable future.

Are Ornate and Desert box turtles the same species? Genetically, yes — they collapse to Terrapene ornata with no subspecies. Behaviourally and ecologically, populations from the Sonoran Desert and the central Great Plains still differ in important husbandry-relevant ways (humidity tolerance, brumation depth). For keepers, the husbandry distinction is more useful than the taxonomic one.

If a paper after 2013 disagrees with Martin et al., what do I do? Trust the most recent paper that has not been substantively challenged by a peer-reviewed response. The 2014 Spinks paper and the 2020 Martin follow-up both broadly support the 2013 framework, with refinements rather than reversals. The Turtle Taxonomy Working Group’s annual checklist is the consensus document and the right citation for most purposes.

Will there be more changes? Almost certainly. Cheaper sequencing, museum specimen re-sampling, and ancient DNA from sub-fossil material will keep refining the picture. The Florida (bauri) and Coahuilan (coahuila) positions are particularly active research areas. Don’t memorise these names like they’re fixed — track the underlying animals.

Does any of this affect captive husbandry? Not directly. The care requirements for a Three-Toed box turtle in 2010 are the same as for a Terrapene mexicana mexicana in 2026. What the revision changes is the ability to do conservation work at the appropriate biological scale, which matters for the long-term survival of the genus rather than for the animal in your enclosure today.

Further reading on Box Turtles

• North American box turtles — the genus overview
• Asian box turtles (genus Cuora) — the other half of the box‑turtle picture
• Box Turtle Conservation — why these names matter for policy

Primary sources

• Martin, B.T. et al. (2013). Sequence‑based molecular phylogenetics and phylogeography of the American box turtles. Molecular Phylogenetics and Evolution 68(1): 119–134. Full text.
• Spinks, P.Q. et al. (2014). Multilocus phylogeny of the New World mud turtles (Kinosternidae) — and related Terrapene material.
• Turtle Taxonomy Working Group annual checklist — current synonymy at iucn-tftsg.org.

If you spot a citation here we’ve got wrong, or a paper we’ve missed, Hannah is the right person to email — write in via the contact page.