The Calophyllaceae and Hypericaceae are revised for Thailand and their relationships to the Clusiaceae and Guttiferae are briefly
discussed. Thirty-two species are definitively recognised in six genera, namely: Calophyllum L., Kayea Wall., Mammea L. and
Mesua L. in the Calophyllaceae and Cratoxylum Blume. and Hypericum L. in the Hypericaceae. A further four species of Calophyllum
are tentatively noted as likely to occur in Thailand. Descriptions, full synonyms relevant to the Thai taxa, distribution maps, ecology,
phenology, vernacular names, specimens examined and provisional keys are given. All species previously classified in the genus
Mesua have been moved to the genus Kayea, except Mesua ferrea L. Two taxa were found to be endemic to Thailand: Mammea
harmandii (Pierre) Kosterm. and Hypericum siamense N.Robson. The distribution for the families in Thailand was found to vary
with the Thai Calophyllaceae being found mainly in Central and Peninsular Thailand whilst the Thai Hypericaceae were found
mainly in the North and the North-East of Thailand. Overall the numbers of collections housed in herbaria are few and more collections
are necessary in order to give a comprehensive account of their distributions in Thailand.