from French Guiana is described and illustrated, and its taxonomic affinities are discussed. Also, a key to the species of Byttneria that occur in the Guianas is provided. The genus Byttneria Loefl. (Sterculiaceae) includes about 130 to 140 species distributed throughout the tropics. The genus is thought to have originated in the Americas, but at present there are three centers of species concentration: the Amazonian Hylaea, Madagascar, and Southeast Asia (Cristobal, 1976). All of the species described heretofore are lianas or shrubs with the possible exception of B. fruticosa Schumann ex Engl. and B. glabra Schumann & Engl. (both sect. Vahihara Arenes). These two East African species were described as small or shrubby trees. Exploration by Scott Mori and collaborators in French Guiana however has yielded a new, arborescent species of Byttneria. Terminology, especially that relating to floral morphology, in the ensuing description follows Cristobal (1976). Leinfellner (1960) may also be consulted for a discussion of floral development and morphology in Byttneria.