The Malesian species of five relatively unknown Euphorbiaceous genera are redescribed. Alphandia, Borneodendron, Cladogynos and Tapoïdes, each with one species in Malesia, are part of the Euphorbiaceae in the strict sense; Ashtonia (two species) is presently classified in the Phyllanthaceae. The descriptions have been completed by studying extra material, and high quality drawings are added.