In places of rich biodiversity increasingly endangered by habitat loss and degradation, it is an urgent matter to assess threats to species uniquely found there and identify areas where a significant proportion of these species are harboured. Borneo has exceptionally high plant diversity and about one-third of its species are endemic. Among these, a subset belongs to endemic genera which are a small but distinctive part of the island’s still incompletely-known flora.
A review of the Bornean endemic plant genera is timely because recent advancements in molecular techniques, together with sustained taxonomic work and botanical collecting, have led to previously endemic genera being subsumed within more widespread genera, alongside new endemic genera being described. Through critically examining morphological and molecular evidence in the literature and close studies of herbarium material, 62 vascular plant genera are presently recognised as endemic to Borneo, from 25 families and comprising 162 known species. Three-quarters of the genera (47 genera) have had at least one species sampled in molecular phylogenetic studies, which includes 28 monotypic and 10 polytypic genera that have been sufficiently sampled to be considered monophyletic with high confidence. In all, 40 of the 62 endemic genera are monotypic (known from a single species only).
Based on this updated list of the endemic genera and their species, centres of endemism in Borneo are identified, defined as areas where the greatest number of species of endemic genera are found. Occurrence records gathered from taxonomic specialist-determined collections and herbarium specimens are used to map and model species distributions, which are then superimposed to represent patterns of species richness. Centres of endemism are found especially in the lowland forests of northwest Borneo, reaffirming the significance of this phytogeographical province. Variables representing climatic conditions and habitat characteristics are also examined for how they are correlated with the centres of endemism.
The species distributions and centres of endemism thus resolved are used to assess plant conservation exigencies for Borneo. Species distributions are compared against land cover and existing protected areas and are used to make provisional IUCN Red List conservation assessments. Prioritisation analyses are conducted to identify areas of remaining forest crucial for protecting as many species of the endemic genera as possible. It is revealed that the centres of endemism occur mostly in forests outside of existing protected areas and which have been logged. These findings reaffirm the critical need for remedial conservation action to safeguard Borneo’s lowland forest habitats and some of its most unique plant species.