A comprehensive investigation of the population genetics and autecology of the endemic New Zealand shrub epiphyte Pittosporum cornifolium (Pittosporaceae) is presented. Pittosporum cornifolium has a wide geographic range and is well adapted to a variety of lifestyles namely terrestrial, rupestral, and more commonly, epiphytic. The primary habitats of P. cornifolium are lowland and coastal ecosystems which, in recent times (<200 years) have been subjected to widespread clearance and fragmentation resulting in major reductions to the species potential population range. The study focused on five populations in the North Island from Coromandel to Taranaki where habitat loss of lowland and coastal ecosystems has been significant. Population-level genetic analysis using Inter-Simple Sequence Repeat (ISSR) markers revealed that while P. cornifolium exhibited high genetic diversity at the species-level, genetic diversity was relatively low at the population-level. The outcrossing dioecious breeding system and unique evolutionary history of P. cornifolium are likely to be key factors influencing the observed high intra-specific diversity whereas reduced genetic diversity at population-level is probably due to geographic isolation caused by recent habitat fragmentation. Ecological parameters were investigated to determine the current ecological status of the five populations and results did not reveal any substantial ecological impediments to regeneration and dispersal modes. Ecological data were incorporated with information from national data sets to provide a more comprehensive overview of P. cornifolium autecology and to develop a predicted environmental distribution map. Key findings indicate P. cornifolium is typically affiliated with old growth forest systems and well drained low nutrient substrates, while low mean daily temperatures (<0.6°C) restrict environmental distribution. Both genetic and autecological research was applied to determine levels of intra-specific divergence in cultivated P. cornifolium individuals from the Poor Knights Islands (outer Hauraki Gulf), which are morphologically distinct from mainland forms. The Poor Knights Islands individuals were the most genetically distinct as revealed by ISSR analysis, having higher pairwise levels of genetic distance than iii mainland populations as well as more unique loci. A single mutation in the sequence of the Internal Transcribed Spacer (ITS) region was revealed in the Poor Knights Islands individuals, distinguishing them from mainland P. cornifolium and additional members of a monophyletic clade which have shared ITS sequences. Furthermore, P. cornifolium from the Poor Knights Islands have significant morphological and anatomical differences such as larger leaves and leaf tissue depths. Long term isolation on the offshore islands is likely to have had the most significant effect on this population divergence. The differences in the Poor Knights Islands individuals may warrant the delineation of a new subspecies or even species. However, a more comprehensive examination of the taxon across its mainland range, the Poor Knights Island group, and other northern offshore islands where the species is present is recommended to clarify current inferences. The results of this research have provided a framework for the development of species specific conservation and restoration strategies for P. cornifolium and reveal the importance of provenance and microhabitat (lifestyle) when sourcing seed for reintroduction projects.