• conservation;
  • Palmae;
  • species;
  • taxonomy

The palm genus Areca is widespread in tropical Asia and includes the economically important betel nut palm, A. catechu. The genus has three centres of high species diversity: the Sunda Region, the Philippines and East Malesia (to the east of Wallace's line). The taxonomy of the genus in East Malesia has been neglected. Prior to this study, 19 species were accepted for this area, all but one endemic, but their limits and differences were not understood. Here, we provide a taxonomic monograph of East Malesian Areca spp., based on an extensive study of the genus in herbaria and in the field. We recognize six species of Areca in East Malesia, including the widespread cultivated A. catechu. Five wild species are accepted, namely A. macrocalyx, A. mandacanii, A. novohibernica, A. oxycarpa and A. vestiaria. We place 12 of the previously accepted species into synonymy, and provide additional new synonymy in A. catechu. © 2011 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 168, 147–173.