The Fifth Labour of Heracles: Cleaning the Linnean stable of names for grass snakes (Natrix astreptophora, N. helvetica, N. natrix sensu stricto)

We scrutinize scientific names erected for or referred to Natrix astreptophora (Seoane, 1884), Natrix helvetica (Lacepède, 1789), and Natrix natrix (Linnaeus, 1758). As far as possible, we provide synonymies for the individual subspecies of each species, identify each name with one of the mtDNA lineages or nuclear genomic clusters within these taxa, and clarify the whereabouts of type material. In addition, we feature homonyms and names erroneously identified with grass snakes. For Natrix astreptophora (Seoane, 1884), we recognize a second subspecies from North Africa under the name Natrix astreptophora algerica (Hecht, 1930). The nominotypical subspecies occurs in the European part of the distribution range (Iberian Peninsula, adjacent France). Within Natrix helvetica (Lacepède, 1789), we recognize four subspecies. The nominotypical subspecies occurs in the northern distribution range, Natrix helvetica sicula (Cuvier, 1829) in Sicily, mainland Italy and adjacent regions, Natrix helvetica cetti Gené, 1839 on Sardinia, and Natrix helvetica corsa (Hecht, 1930) on Corsica. However, the validity of the latter subspecies is questionable. For Natrix Cetti Gené, 1839, we designate a lectotype from Sardinia to stabilize current usage of this name. Furthermore, we give Coluber siculus Cuvier, 1829 and Tropidonotus natrix var. astreptophorus Seoane, 1884 precedence over four previously overlooked senior synonyms that we qualify as nomina oblita according to the requirements of the International Code of Zoological Nomenclature. Coluber bipedalis Bechstein, 1802 and Vipera vissena Rafinesque, 1814 are nomina oblita for Coluber siculus Cuvier, 1829. Coluber distinctus Gravenhorst, 1807 and Tropidonotus sparsus Schreiber, 1875 are nomina oblita for Tropidonotus natrix var. astreptophorus Seoane, 1884. For Natrix natrix (Linnaeus, 1758) we recognize tentatively five subspecies, some of which hybridize broadly. The nominotypical subspecies matches the 'yellow mtDNA lineage' and the 'yellow microsatellite cluster' and lives in Scandinavia and Central Europe. For Natrix vulgaris Laurenti, 1768, we designate a neotype and resurrect this name for the previously characterized 'red mtDNA lineage' of Natrix natrix that also corresponds to a distinct nuclear genomic cluster (Natrix natrix vulgaris Laurenti, 1768). Pure populations of this subspecies are restricted to southern and southeastern Central Europe. The 'green mtDNA lineage' of Natrix natrix, also distinct with respect to nuclear genomic markers, corresponds to Natrix natrix scutata (Pallas, 1771). This subspecies occurs in most of the eastern distribution range. Natrix natrix persa (Pallas, 1814) is characterized by another mtDNA lineage endemic to the Transcaucasus und northern Iran. We restrict this subspecies to populations in these regions, while the taxonomic status of grass snakes from the Balkans and Asia Minor, previously also assigned to Natrix natrix persa, demands further research. Finally, we tentatively recognize Natrix natrix syriaca (Hecht, 1930) as valid. This subspecies is characterized by yet another mtDNA lineage endemic to southeastern Turkey. Based on genetic evidence, the following subspecies should not be recognized: Natrix natrix fusca Cattaneo, 1990, Natrix natrix gotlandica Nilson & Andrén, 1981, and Natrix natrix schweizeri Müller, 1932. Some other names can be unambiguously identified with distinct mtDNA lineages and could represent distinct taxa. However, without additional nuclear genomic evidence, we refrain from potentially premature taxonomic decisions