Ovary anatomy and organography was investigated in five species of Heliconia (Heliconiaceae) and three species of Musa (Musaceae). The ovaries of both genera may be longitudinally divided into three regions: sublocular, locular, and prolongation. The prolongation is the elongated closure of the top of the locules. The proportions of these regions differ between genera and to a lesser extent among species within a genus. In general, Heliconia has a larger sublocular region while the prolongation is larger in Musa. These differences are correlated with the occurrence of gynopleural nectaries in the sublocular region of the Heliconiaceae and in the prolongation of the Musaceae. Anatomical and organographic details are related to our knowledge of the development of the ovary and fruit. Many anatomical differences between the genera are correlated with the functions of these regions in the fruit. The structure and homology of the placental trichomes of the Musaceae are discussed, and I conclude that they are not homologous to the arils of the other Zingiberales. Key words: plant morphology, plant anatomy, nectaries, monocotyledons.