The present paper is an extension of my revision of the Malaysian species of the genus Dillenia L. (Wormia Rottb. included) inserted in the revision of the Dilleniaceae in the Flora Malesiana ser. I, vol. 4, part 3, pp. 141—174, published in December 1951. A critical revision of the whole genus has never been published before; the unfortunate result of this has been that the delimitation of Dillenia and Wormia, usually as distinct genera, has been based on different characters by various authors. The extension of the revision for the Flora Malesiana so as to include the extra-malaysian species enabled me to study a number of species, the knowledge of which certainly confirmed me in my idea that the characters on which Dillenia and Wormia had been separated before are certainly not the primary characters, to be used in the taxonomic treatment of the genus. All specimens and literature mentioned in this work have been examined by me, unless indicated otherwise; excepted are the specimens of the U.S. National Herbarium., of which I have only examined those collections, of which no duplicates were available from other herbaria. Particulars, not to be taken from the herbarium specimens themselves, such as habit, height, diameter, colour, etc., have been taken from the collectors’ notes and, as far as reliable, from the literature, and are inserted in the descriptions; if there are contradictory data, they are discussed under the Notes.