The floral development and anatomy of Carica papaya (Caricaceae)

Floral development and anatomy of Carica papaya L. have been investigated t o shed light on (i) the morphology of the flower, (ii) the structural basis for the pollination mechanism, and (iii) the relationships of the Caricace ae. Carica is mostly dioecious with a strong dimorphism between staminate a nd pistillate flowers. The development of staminate flowers resembles that of pistillate flowers up to the initiation of the stamens. Further developm ent leads to highly diverging morphologies. In staminate flowers a combinat ion of contorted growth and the development of a common stamen-petal tube p roduces a long floral tube. The gynoecium grows into a central spearlike pi stillode. The pistillate flowers have no traces of stamens and initiate fiv e antesepalous carpel primordia. Common basal growth leads to the developme nt of a large ovary with staglike stigmatic lobes and intruding placentas c overed with numerous ascending ovules. Floral anatomy of staminate and pist illate flowers is described. The nature of the colleters is discussed. The morphological basis for reward production in C. papaya is clarified, and co nflicting views on pollination are discussed. Nectaries of staminate flower s are located on the central rudimentary pistil and not at the base of the stamens, as previously reported. The anthers contain packages of calcium ox alate crystals. Pistillate flowers produce no nectar but have a stigmatic e xudate. We compared the floral development and anatomy of Carica with that of Adenia (Passifloraceae) and Moringa (Moringaceae) in the view of a relat ionship with other glucosinolate-producing families. Although a derivation of the unisexual flowers from bisexual ancestors is probable, Storey's hypo thetical derivation of pistillate flowers is not supported by the floral on togeny and vasculature.