Naultinus is a genus of geckos that are endemic to New Zealand. On account of their striking colouration, species in the genus Naultinus are commonly known as green geckos. There are nine described species in the genus. Species in the genus share a number of traits that set them apart as quite different from the rest of the world's two thousand odd gecko species, which are generally brown in colour, ovivaparous, short-lived and nocturnal. In contrast, Naultinus are green (with the exceptions of males in two South Island species which exhibit sexual dimorphism in colouration), ovovivaparous, live up to 30 years or more and are strictly diurnal. New Zealand has a temperate, maritime climate, and in terms of distribution Naultinus is one of the southernmost gecko genera in the world — some species live in habitats in the South Island which receive regular snowfall in winter. Animals in this genus possess several physiological and behavioural adaptations to cope with these periods of low temperatures and adverse weather.
While historically widespread and quite common in areas of native forest all over the country, all species in this genus are of conservation concern in the present day. All nine species of Naultinus are declining in the wild and are much harder to find than they used to be; the populations of the various species are highly fragmented and approaching extinction, while others in the genus have already gone extinct. Entire populations of certain species, with unique traits and distinctive genetic profiles, have disappeared in the last 20 years. The primary known agents of this catastrophic decline include predation by invasive mammalian and avian species, habitat destruction and poaching for the illegal pet trade. Vespid wasp predation is speculated to be another possible contributing cause. Legal protection in the form of longer prison sentences for poachers caught with New Zealand protected species has been increased in recent years and translocations of various species to pest free islands have been undertaken with mixed results, but the task of saving these animals remains daunting. The behavioural and visually cryptic nature of these animals also pose challenges to their conservation management. The genus is, in general, in "dire need of research, particularly into factors that are causing their apparent decline", certain aspects of which remain unexplained.
The nine described species of Naultinus are found throughout the North and South islands of New Zealand and on a number of offshore islands. Historically, Naultinus species lived throughout the length of New Zealand, from the coast to as much as 1400 metres above sea level. However, all species have now undergone massive declines, and populations nationwide are fragmented and few (see "Conservation") Four species; elegans, grayii, flavirictus and punctatus are found only in the North Island. What was previously thought to be a distinct population of grayii, found only in the far north on the Aupouri Peninsula has been determined from genetic work in the early 2000s to be a new species, more closely related, in fact, to elegans. It was described as N. flavirictus in 2021. The remaining five species: gemmeus, manukanus, rudis, stellatus, and tuberculatus are found only in the South Island. South Island Naultinus were, in the past, placed in a separate genus called Heteropholis but this taxon was abandoned when new genetic research in the 1980s showed little phylogenetic basis for this taxonomic division.
None of the Naultinus gecko populations are sympatric, presumably because each species is very finely adapted to its local environment and also because their respective ecological niches are incredibly similar.
Habitat destruction by the encroachment of suburban areas into forested Naultinus habitat both directly destroys the ecosystems in which the animals live, as well as also facilitating further decline by increasing the size of local cat and rodent populations. A unique population of Naultinus gemmeus near Hakatarema Pass, east of Twizel which displayed unusual colouration and a distinctive genetic profile was entirely destroyed when its forest habitat was cleared by a bulldozer for urban development.