Of about a hundred species formerly recognized in Sapium Jacq. (Euphorbiaceae tribe Hippomaneae), twenty one species are retained in this genus. As defined in the present monograph, the genus Sapium is restricted to the neotropics. Palaeotropical taxa previously assigned to Sapium are transferred to Anomostacbys (Baill.) Hurus. (1 sp.), Duvigneaudia J. Léonard (2 spp.), Sclerocroton Hochst. (6 spp.) and Shirakia Hurus. (8 spp.). All of these genera are fully treated with the exception of Shirakia which is preliminarily revised. A new generic classification is presented using cladistic analysis. A brief review of the theoretical foundations of cladistic methodology leads to the conclusion that parsimony should be favored over compatibility analysis.