The genus Trymatococcus has been published in 1838 by Poeppig and Endlicher in Nova Genera ac Spec. Plant II. p. 30, and the genus was based on the species T. amazonicus. In 1876 Baillon added the species T. africanus to the genus. This gave a peculiar distribution for a genus with two species only: one in the Amazone region and one in West Africa. Later on several new species from Africa were described: three by Engler (T. kamerunianus, dorstenioides, and Conrauanus), one by De Wildeman (T. Gilletii) and one by Pellegrin (T. oligogyna). In 1922 (Archivos do Jardim Botanico Rio de Janeiro vol III. p. 22) Ducke described a second species from Amazonian Brazil (T. paraensis) and said in the notes to this new species that Lanessania turbinata Baill. should be transferred to the genus Trymatococcus and published a new combination (T. turbinatus Ducke). In 1925 (Archives IV. p. I) he emphasized his statements Trymatococcus and published a new combination (T. turbinatus as well as turbinatus and amazonicus have the stamens erect in the bud and not inflexed as was described in the former publications. He also emphasized that the place of Trymatococcus in the system has to be changed and the genus has to take the place taken up to this moment by Lanessania. Among the material of the Moraceae from Surinam which I am studying for the Flora of Surinam, I found also a Trymatococcus species. By the study of this genus I was struck by the peculiar geographic distribution of the genus, which fully supported my observations on the Euphorbiaceae (cf. Lanjouw, The Euphorbiaceae of Surinam pp. 70—84). For the preparation of a map of this distribution I studied the african species and after a careful examination I noted a number of important differences between the african species and the american ones. Part of these differences were never noticed before and no attention has ever been given to these facts. The first error in this case was made by Baillon. Most probably he had not seen T. amazonicus Poepp. et Endl. when he described his T. africanus. This is still more striking as he described in the same paper his genus Lanessania based on L. turbinata, which is a true Trymatococcus species. It is very curious that it was not possible for Baillonto observe his mistake because in his Histoire des Plantes (vol. VI. p. 199) he states „filamentis aestivatione inflexis vel nunc suberectis”. One can not understand why he did not observe that at least one of the species of Trymatococcus is the same as his genus Lanessania. After Baillon’s publication, we could say that we had got two type species, one american (Tr. amazonicus Poepp. et Endl.) and one african (Tr. africanus Baill.). Apparently Engler did not study exactly Tr. amazonicus Poepp. et Endl. when he described his new species though he states (Monogr. Afr. Pfl. fam. I. Morac. p. 28); ”Ein besonders auffallender Unterschied im Bau der Blüte und Frucht is nicht zu constatieren; bei der amerikanischen Art sind die männlichen Blüten dreimännig mit dreiteiliger Blütenhülle, bei den afrikanischen Arten sind sie zweimännig”. Likewise Ducke knew apparently only the american species when he pointed out the new place for this genus in the family. By these reasons only it is explained how confusion has crept into this genus. I have studied many specimens of Trymatococcus from the following herbaria: Berlin-Dahlem, British Museum (Natural History Museum), Kew, Leiden, Paris and Utrecht. I wish to express mv sincere thanks to the directors for their hospitality or fore sending the material on loan.