Plant Endemism, Rarity, and Threat in Palau, Micronesia: A Geographical Checklist and Preliminary Red List Assessment

An official checklist of the endemic plant species of Palau has been long awaited, and is presented here for the first time. For each species a substrate limitation, growth form, and relative abundance is listed. In addition an IUCN red list assessment was conducted using all available data. For over half of the endemic species there is insufficient data to provide a red listing status however an expected minimum number of threatened plants out of the total is inferred. Approximately 15% of Palau's endemic plants are believed to be only known from the type collection and many more only known from a few collections. These taxa however may now be prioritized and targeted for future inventory and research. The taxonomic robustness of several of these taxa is questionable and it is expected that more endemic species will be lost to synonymy in the future. Previous estimations have significantly over-estimated the rate of plant endemism in Palau (e.g., 194). Here it is established that the rate of plant endemism (130) is comparable to some of its neighboring Micronesian islands to the east, notably Guam and Pohnpei. Several species are known to be restricted to isolated disjunct populations however the causes for their rarity are poorly known and have never been intensively studied. Palau although notable for its high percentage of remaining primary forest compared to other oceanic islands faces increasing threat from development making these small populations highly vulnerable. Nothing is known about how these rare species will respond to the imminent threat of climate change. There is no current legislation protecting specific plant species as their rarity has never been systematically quantified. This paper represents a step towards plant conservation in Micronesia and it aims to stimulate further studies to address the data deficiencies documented here.