A skeletal world revision of the genus is presented to accompany a family account for Flora Malesiana. 82 species are recognised, of which 74 occur in the Malesiana region. Six species are described as new, one species is raised from infraspecific status, and five species are restored from synonymy. Many names are typified for the first time. Three widespread, or locally abundant hybrids are also included. Full descriptions are given for new (6) or recircumscribed (7) species, and emended descriptions of species are given where necessary (9). Critical notes are given for all the species. Little known and excluded species are discussed. An index to all published species names and an index of exsiccatae is given.