Among the Nyctaginaceae the genus Pisonia is the only one that has produced an appreciable number of species outside the New World. Some of these have very wide areas in the Pacific and along the borders of the Indian Ocean, others occupy smaller areas, mostly m eastern Malesia, Melanesia, and Polynesia. In Australia there are three species, in the north the circumtropical P. aculeata L., in the north and east P. umbellifera Seem, and P. grandis R. Br. In Africa there is only one circumtropical species in the eastern coastal parts, viz. P. aculeata L., further in the Malesian area two widely distributed Old World species, viz. P. umbellifera Seem, and P. grandis R. Br. occur. This revision contains a brief taxonomic discussion of the infrageneric subdivision. Calpidia, Ceodes, and Rockia are merged with Pisonia. In all 13 species are distinguished, for which keys, synonymy, and typification are provided. Of the five extra-Malesian species a description is given. Four new combinations have been made. I have to express my thanks to the Directors of the Herbaria at Florence, Paris, Singapore, Utrecht, and the Curator of Collections, Bernice P. Bishop Museum, Honolulu, for the privilege of examining their collections. Besides, I have to thank Dr R. Melville of Kew and Dr H. Heine of Paris, for providing valuable information, to Mr M. Jacobs for considerable help and criticism, and to Dr van Steenis for supervising and editing this work.