How many genera of vascular plants are endemic to New Caledonia? A critical review based on phylogenetic evidence

New Caledonia is a biodiversity hotspot located in the south-western Pacific, well known for its rich, unique and endangered flora. The island flora has a high level of endemism not only at the species level (75%), but also at the generic and family (three endemic) levels. We review here the taxonomic validity of the c. 100 endemic New Caledonian genera of vascular plants (13%) by using the monophyly criterion based on the available phylogenetic data. As observed in other island floras, some of these genera were recovered nested in larger genera and are consequently likely to lose their rank. After a critical review, we concluded that the New Caledonian plant vascular flora contains between 62 and 91 endemic genera. This large variation in the number of endemic genera is mainly caused by a lack of DNA sequences (eight genera) and limited phylogenetic evidence. This work highlights gaps of knowledge that will have to be addressed to stabilize the taxonomy of the New Caledonian flora. Although this study shows that several genera are not monophyletic, New Caledonia still harbours more endemic genera than any other islands in the Pacific Ocean. Preliminary results indicate that the high level of endemism at higher taxonomic levels could be explained by an accumulation of relictual lineages, rather than adaptive radiations. Hypotheses explaining this phenomenon are provided in this study.