Generic delimitation within the Trichilieae (Meliaceae) is considered, with particular reference to the Trichilia P. Browne - Heynea Roxb. ex Sims - Walsura Roxb. complex. Original investigations of leaf-surface micromorphology, palynology and fruit anatomy are made of species of each genus of the tribe and an isoenzyme study is made of species of Trichilia. Heynea and Walsura. The accounts of these studies are extensively illustrated with photographs, scanning-electron-micrographs and annotated drawings. Seed dispersal systems are briefly considered including original field observations of a species of Walsura. In the light of the data revealed by these studies, inter-generic relationships are discussed. The Indo-Malesian genus Walsura is taxonomically revised and the closely related new genus Pseudoclausena is segregated from it and described. Within Walsura. a new section (Ruswala) and three new species (W. dehiscens. W. pachycaulon and W. sarawakensis) are described and one new combination is made (W. trifoliolata ssp. acuminata). The new genus consists of one new species (P. chrysogyne). formerly W. chrysogyne (Miq.) Bakh.f, and W. velutina Ridley is reduced to a new forma of it. Keys are given for the identification of all taxa and the species are illustrated by drawings and (in some cases) by photographs. A cladistic analysis is made of all the species of Walsura. Pseudoclausena and Heynea. taking Trichilia as the outgroup. This, together with the findings of the above studies and published data indicate that Heynea should be considered a distinct genus in the alliance of Walsura. A key for the identification of these four genera is given. The other genera of the tribe are briefly considered and all are maintained as distinct. The great diversity of fruit structures within the tribe provides particularly good characters for the segregation of these genera.