Floral development and anatomy of Carica papaya L. have been investigated to shed light on (i) the morphology of the flower, (ii) the structural basis for the pollination mechanism, and (iii) the relationships of the Caricaceae. Carica is mostly dioecious with a strong dimorphism between staminate and pistillate flowers. The development of staminate flowers resembles that of pistillate flowers up to the initiation of the stamens. Further development leads to highly diverging morphologies. In staminate flowers a combination of contorted growth and the development of a common stamen-petal tube produces a long floral tube. The gynoecium grows into a central spearlike pistillode. The pistillate flowers have no traces of stamens and initiate five antesepalous carpel primordia. Common basal growth leads to the development of a large ovary with staglike stigmatic lobes and intruding placentae covered with numerous ascending ovules. Floral anatomy of staminate and pistillate flowers is described. The nature of the colleters is discussed. The morphological basis for reward production in C. papaya is clarified, and conflicting views on pollination are discussed. Nectaries of staminate flowers are located on the central rudimentary pistil and not at the base of the stamens, as previously reported. The anthers contain packages of calcium oxalate crystals. Pistillate flowers produce no nectar but have a stigmatic exudate. We compared the floral development and anatomy of Carica with that of Adenia (Passifloraceae) and Moringa (Moringaceae) in the view of a relationship with other glucosinolate-producing families. Although a derivation of the unisexual flowers from bisexual ancestors is probable, Storey's hypothetical derivation of pistillate flowers is not supported by the floral ontogeny and vasculature.Key words: Adenia, Caricaceae, Moringa anatomy, calcium oxalate packages, dioecy, floral structure, nectaries, ontogeny, pollination, systematic relationships.