In the Flora Malesiana Backer and van Steenis (1951) recorded five species of the genus Sonneratia, three of which occur in Malesia, viz. S. caseolaris (L.) Engler, S. alba J. E. Smith, and S. ovata Backer. In the course of a palynological study of recent and fossil Sonneratia pollen (Muller, 1964), it was discovered that in Brunei, NW. Borneo, hybridization occurs between these species. It is the purpose of this note A. to describe the morphology of the hybrids, and B. to report on a preliminary cytological examination of the species and the hybrids for determining the chromosome numbers and for detecting irregularities in chromosome behaviour at meiosis in the hybrids.