A comprehensive taxonomic revision of the genus Dasymaschalon (Annonaceae) in Thailand is presented. Twelve species are recognized, including five that are newly described and one new nomenclatural combination, viz. D. acuminatum sp. nov., D. angustifolium sp. nov., D. dasymaschalum, D. echinatum sp. nov., D. filipes, D. glaucum, D. grandiflorum sp. nov., D. lomentaceum, D. macrocalyx, D. obtusipetalum sp. nov., D. sootepense, and D. wallichii comb. nov. Previous taxonomic confusion regarding the relationship between Dasymaschalon and Desmos is discussed. The most significant diagnostic difference between the two genera is the number and arrangement of petals: Dasymaschalon species have only three petals (homologous with the outer whorl of other Annonaceae) that are apically connivent to form an enclosed pollination chamber, whereas Desmos species have two whorls of three petals which are basally constricted and apically free.