Some time ago the “Institute Agronómico do Norte, Belem, Pará, Brazil” sent me a set of specimens for identification among which I detected a new species of Henriquezia Spruce ex Bth. This discovery induced me to study once more and now in somewhat more detail the relation between this genus and the nearly related Platycarpum Humb. et Bonpl. and the position these two genera occupy with regard to the habitually rather similar Gleasonia Standl., a subject to which I had already paid some attention at an earlier occasion, and on which I had reported in a note which is to be found at the base of p. 16 of my work on “the African Species of Oldenlandia L sensu Hiern et K. Schumann” in Verh. Kon. Ned. Akad. v. Wetensch., Sect. 2, 48, no 4, 1952. By the good office of Dr Bassett Maguire I received on loan from the New York Botanical Garden the rich materials by which, as a result of the Botanical Garden’s recent expeditions to Tropical America, these genera are represented in its herbarium, and during a recent visit to England I could study also the valuable collections in the herbarium of the Royal Botanic Gardens, Kew. In the course of these studies I discovered among the Platycarpum specimens too a new species. Descriptions of the latter and of my new Henriquezia will be found further on in this paper. They are, however, but of secondary importance; the main object of this study is to ascertain as precisely as possible the taxonomical position of these three rather puzzling genera. In the note on p. 16 of my work on “the African Species of Oldenlandia L sensu Hiern et K. Schumann” I stated that Gleasonia Standl. “on account of the large and flat exalbuminous seeds and also because of the very peculiar structure of the testa is to be referred to the Henriquezieae, a tribe that will have to be removed as a separate family to the Tubiflorae.” In support of this opinion I referred to Fig. c, d, e and f of Tab. V, which represent the testa of Henriquezia verticillata Spruce ex Bth., of Platycarpum orinocense Humb. et Bonpl. and of two species of Gleasonia, viz. Gl. uaupensis Ducke and Gl. macrocalyx Ducke.