They are small tortoises, ranging in length from 7 cm to 35 cm and in weight from 0.7 kg to 7 kg, although the extinct T. atlas[verification needed] reached 2.5 m. Like most tortoises, they are herbivorous.
Synonymies on Testudo are notoriously difficult to compile with any degree of accuracy. The status of species referred have undergone a great many changes, each change introducing an additional level of complexity and making bibliographic research on the taxa extremely difficult. Most early and not a few later checklists contain a very high proportion of entirely spurious entries, and a considerable number of described species are now considered invalid - either because they are homonyms, non-binomial or for some other reason.
Since then, DNA sequence data has increasingly been utilized in systematics, but in Testudines (turtles and tortoises) its usefulness is limited: In some of these, at least mtDNA is known to evolve more slowly in these than in most other animals. Paleobiogeographical considerations suggest that the rate of evolution of the mitochondrial 12S rRNA gene is 1-1.63% per million years for the last dozen million years or so in the present genus and ntDNA evolution rate has been shown to vary strongly even between different population of T. hermanni; this restricts sequence choice for molecular systematics and makes the use of molecular clocks questionable.
Conventionally, five species are placed here:
- Russian Tortoise or Horsfield's Tortoise, Testudo horsfieldii
- Hermann's Tortoise, Testudo hermanni
- Greek Tortoise or Spur-thighed Tortoise, Testudo graeca
- Kleinmann's Tortoise or Egyptian Tortoise, Testudo kleinmanni
- Marginated Tortoise. Testudo marginata
The first two are more distinct and ancient lineages than the closely related latter 3 species. It was argued that T. horsfieldii belonged in a new genus (Agrionemys) on the basis of the shape of its carapace and plastron, and its distinctness is supported by DNA sequence analysis. Likewise, a separate genus Eurotestudo has recently been proposed for T. hermanni; these three lineages were distinct by the Late Miocene as evidenced by the fossil record. Whether these splits will eventually be accepted remains to be seen. The genus Chersus has been proposed to unite the Egyptian and Marginated Tortoises which have certain DNA sequence similarities, but their ranges are (and apparently always were) separated by their closest relative T. graeca and the open sea and thus, chance convergent haplotype sorting would better explain the biogeographical discrepancy.
On the other hand, the Greek Tortoise is widespread and highly diverse. In this and other species, a high number of subspecies has been described, but not all generally accepted, and several (such as the "Negev Tortoise" and the "Dwarf Marginated Tortoise") are now considered to be local morphs. Some, such as the Tunisian Spur-thighed Tortoise, have even been separated as a separate genus Furculachelys, but this is not supported by more recent studies. However, it is likely that the "Greek" Tortoise will be split into two or more species in the near future.
- Avise, John C.; Bowen, Brian W.; Lamb, Trip; Meylan, Anne B. & Bermingham, Eldredge (1992): Mitochondrial DNA evolution at a turtle's pace: evidence for low genetic variability and reduced microevolutionary rate in the Testudines. Mol. Biol. Evol. 9(3): 457-473. PDF fulltext
- de Lapparent de Broin, France; Bour, Roger; Parham, James F. & Perälä, Jarmo (2006): Eurotestudo, a new genus for the species Testudo hermanni Gmelin, 1789 (Chelonii, Testudinidae). [English with French abstract] C. R. Palevol 5(6): 803-811. doi:10.1016/j.crpv.2006.03.002 PDF fulltext
- Fritz, Uwe; Kiroký, Pavel; Kami, Hajigholi & Wink, Michael (2005): Environmentally caused dwarfism or a valid species - Is Testudo weissingeri Bour, 1996 a distinct evolutionary lineage? New evidence from mitochondrial and nuclear genomic markers. Mol. Phylogenet. Evol. 37(2): 389–401. doi:10.1016/j.ympev.2005.03.007 PDF fulltext
- Fritz, Uwe; Auer, Markus; Bertolero, Albert; Cheylan, Marc; Fattizzo, Tiziano; Hundsdörfer, Anna K.; Sampayo, Marcos Martín; Pretus, Joan L.; Široký, Pavel & Wink, Michael (2006): A rangewide phylogeography of Hermann's tortoise, Testudo hermanni (Reptilia: Testudines: Testudinidae): implications for taxonomy. Zool. Scripta 35(5): 531-548. doi:10.1111/j.1463-6409.2006.00242.x PDF fulltext
- Highfield, A.C. & Martin, J. (1989): A revision of the Testudines of North Africa, Asia and Europe. Genus: Testudo. Journal of Chelonian Herpetology 1(1): 1–12. HTML fulltext
- Khozatsky, L.I. & Mlynarski, M. (1966): Agrionemys - nouveau genre de tortues terrestres (Testudinidae) ["Agrionemys - a new genus of tortoises"]. [Article in French[verification needed]] Bulletin de l'Académie Polonaise des Sciences II - Série des Sciences Biologiques 2: 123-125.
- van der Kuyl, Antoinette C.; Ballasina, Donato L. Ph.; Dekker, John T.; Maas, Jolanda; Willemsen, Ronald E. & Goudsmit, Jaap (2002): Phylogenetic Relationships among the Species of the Genus Testudo (Testudines: Testudinidae) Inferred from Mitochondrial 12S rRNA Gene Sequences. Mol. Phylogenet. Evol. 22(2): 174–183. doi:10.1006/mpev.2001.1052 PMID 11820839 (HTML abstract)
- van der Kuyl, Antoinette C.; Ballasina, Donato L. Ph. & Zorgdrager, Fokla (2005): Mitochondrial haplotype diversity in the tortoise species Testudo graeca from North Africa and the Middle East. BMC Evol. Biol. 5: 29. doi:10.1186/1471-2148-5-29 (HTML/PDF fulltext + supplementary material)