This species is based upon Cinchona grandiflora R. & P. (Fl. Peruv. 2: 54. pl. 198. 1799). In their next volume, Ruiz & Pavon described Cosmibuena obtusifolia (Fl. Peruv. 3: 3. pl. 198. 1802), but this proves to be synonymous with their previously described Cinchona grandiflora. In 1843 Klotzsch in Hayne, Arzney Gewachse 14, sub t. 15. described Cosmibuena quinqueflora from the Andes of Merida, Venezuela, and C. triflora from the Guianas, both of which appear identical with Cinchona grandiflora R. & P. except for the calyx lobes which are obtuse in Cosmibuena quinqueflora. There is some variation, but not significant, in the length of the corolla tube, length and width of corolla lobes, and calyx segments. The number of flowers in an inflorescence varies from three to six on the same branch of the tree and has no taxonomic significance. Measurements of the above-mentioned variation run as follows: corolla tube (4.5 cm long in Cuatrecasas 23788 to 10 cm long in Maguire & Fanshawe 23226), corolla lobes (2-4 cm long by 0.8-1.8 cm (Cuatrecasas 23788) wide, calyx tube (4-7 mm long), calyx lobes lobes 1.5-7 (Cuatrecasas 23788) mm long, petiole (1.1-4 cm long), and leaf width (3-10.5 cm). The corolla tube may vary in length on the same specimen (as in Cuatrecasas 23788 from 4.5-6 cm).
Typical Cosmibuena grandiflora has the calyx lobes acute to acuminate, in this respect only differing from Buena latifolia Benth., Cosmibuena latifolia Klotzsch, and C. quinqueflora. I have taken up the variations with obtuse calyx lobes and treated them as a variety of C. grandiflora.