(The contents of this contribution are treated more fully in Kew Bulletin 17, 381-396 (1964) and in a further paper to be published in that journal. A summary only, therefore, is presented in this present account.) A new genus of Fagaceae, Trigonobalanus Forman, was discovered on Mt Kinabalu by the 1961 Royal Society Expedition to North Borneo. Tr. verticillata Forman, now also known to occur in Malaya and Celebes, is most remarkable in having leaves in whorls of three with connate inter-petiolar stipules—characters hitherto unknown in the family. A second species from northern Thailand, Tr. doichangensis (A. Camus) Forman ( = Quercus doichangensis A. Camus), has been added to the genus.