The genus Triturus is currently regarded as having fifteen species. These are usually divided into two groups- the large-bodied newts, and the small-bodied newts. Two species (T.alpestris and T.vittatus) are intermediate in size, although are considered to be more closely related to the large-bodied group. The species cristatus, carnifex, dobrogicus, ivanbureschi, karelinii and macedonicus are all very similar in appearance, and were once regarded as subspecies of T. cristatus. Similarly, T. marmoratus and T. pygmaeus were previously subspecies of T. marmoratus. All fifteen species are listed below.
Recent work on Triturus species (e.g. García-París et al., 2004, Litvinchuk et al., 2005) suggests that it may be appropriate to divide the genus into separate genera. This is because some Triturus species appear to be more closely related to species from other genera (e.g. Euproctus, Neurergus) than they are to other Triturus species.
García-París et al. have proposed splitting the genus into three genera, Triturus being retained for the large-bodied group, including T. vittatus. Mesotriton is proposed for T. alpestris, and Lissotriton for the remaining species.
Litvinchuk et al. describe a scheme where Triturus is retained for the large-bodied group, Ommatotriton is proposed for T. vittatus, Mesotriton is proposed for T. alpestris, and Lophinus includes the remaining species.
Litvinchuk et al. also propose splitting vittatus into two species, Ommatotriton vittatus for the Southern populations, and Ommatotriton ophryticus for the Northern populations. A new subspecies, O. ophryticus nesterovi, is also proposed for the Western part of the distribution of O. ophryticus.
The degree of acceptance of either of these schemes remains to be seen.
Older publications may use different specific names for some of the species; T. palmatus was sometimes used for T. helveticus, T. taeniatus was used for T. vulgaris, and T. blasii was used to describe the natural hybrid between T. cristatus and T. marmoratus. In addition, other species were included in the genus, which are now considered to belong to other genera; the genera Notophthalmus and Cynops are two such examples. Very early writings used Triton instead of Triturus.
Despite the presence of so many species in Europe, there is limited overlap between species, and the largest number present in one area is five (Arntzen and De Wijer, 1989). This maximum concentration occurs in northwest France, at the overlap of the range of T. marmoratus and T. cristatus, where T. alpestris, T. vulgaris, and T. helveticus also occur. Even where this many species occur, differing habitat preferences may mean that there is little actual contact between newts of different species.
Note: the distribution maps on the species pages are adapted from those published in Macgregor, Sessions and Arntzen (1990).
Arnold & Burton (1978) give some detail on identifying Triturus species by skull features:
"Two of the bones on each side of the skull, the frontal and the squamosal, often have projections that may meet to form a structure called the fronto-squamosal arch. Sometimes the arch is completely bony, but often it is interrupted in the middle or is entirely absent. Among European species, the structure usually varies as follows (Fig., below):
Arnold, E. N., & Burton, J. A., 1978. A Field Guide To The Reptiles And Amphibians Of Britain And Europe. Collins, London
Arntzen, J. W., & De Wijer, P., 1989. On the distribution of the Palaearctic Newts (genus Triturus) including the description of a five species pond in Western France. British Herpetological Society Bulletin 30: 6-11
García-París, M., Montori, A., & Herrero, P., 2004. Amphibia: Lissamphibia. Fauna Ibérica, Vol. 24. Museo Nacional de Ciencias Naturales, Madrid.
Litvinchuk, S. N., Zuiderwijk, A., Borkin, L. J., & Rosanov, J. M., 2005. Taxonomic status of Triturus vittatus (Amphibia: Salamandridae) in western Turkey: trunk vertebrae count, genome size and allozyme data. Amphibia-Reptilia 26(3):305-323.
Macgregor, H. C., Sessions, S. K.,
& Arntzen, J. W., 1990. An integrative analysis of
phylogenetic relationships among newts of the genus Triturus
(family Salamandridae), using comparative biochemistry,
cytogenetics and reproductive interactions. Journal of Evolutionary Biology