The
systematics and
taxonomy of
Testudo is notoriously problematic. Highfield and Martin commented: Synonymies on
Testudo are notoriously difficult to compile with any degree of accuracy. The status of species referred has 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 have increasingly been used 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 the rate of evolution of the mitochondrial
12S rRNA gene is 1.0-1.6% 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. The following extant species in the following subgenera are placed here: • Genus
Testudo • Subgenus
Agrionemys •
Russian tortoise or Horsfield's tortoise,
T. horsfieldii 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, == Mating ==