During the process of completing the Rubiaceae Juss. treatment for the Flora of the Guianas, two little-known taxa described from material collected in French Guiana, Mussaenda glomerulata Lam. ex Poir. and Octavia sessiliflora DC, needed to be studied in order to establish their true identity. Mussaenda glomerulata was first studied by Lamarck and later published by Poiret (1797), based on specimens collected by L. C. Richard; a specimen of M. glomerulata was found in the Lamarck herbarium, which is here selected as lectotype. Mussaenda glomerulata was concluded to be synonymous with Amaioua corymbosa Kunth. Because M. glomerulata has priority over Amaioua corymbosa, the new combination Amaioua glomerulata (Lam. ex Poir.) Delprete & C. Persson, comb. nov. is here proposed. The obscure Octavia DC. was published by Candolle based on specimens with ovaries and fruits. After a detailed analysis of the type specimens, we inferred that the flowers of Octavia are always terminal, although sometimes they might appear axillary because of overtopping axillary shoots (pseudoaxillary). Additionally, what Candolle interpreted as 8-merous fruits is a misinterpretation, and they are instead fleshy berries with eight seeds. With these new observations in mind, we concluded that Octavia sessiliflora is synonymous with Cordiera triflora A.Rich in DC. Full synonymy, typification of the taxa involved and representative specimens of this species are here presented.