A revision of the genus Mitragyna (Rubiaceae) in Thailand is reported. Four species, i.e. M. diversifolia, M. hirsuta, M. rotundifolia,
and M. speciosa are described in this taxonomic treatment. A summary of taxonomic history, detailed morphological descriptions,
distributions, ecology, phenology, vernacular names, uses, IUCN conservation status, specimens examined, photographs and a key
to the species are proposed. Two names are lectotypified: M. rotundifolia and M. speciosa.