The Araceae consisting of some 105 genera and over 3300 species is one of the most diverse families of angiosperms in both vegetative and floral morphology. Despite extensive attempts at classification of the family by anatomical and molecular methods little concensus has been reached on the classification of aroids above the tribal level. Part of the difficulty in determining relationships among aroids centers around a general lack of understanding of the types of developmental modifications that have contributed to the tremendous array of floral diversity in the family. Of particular interest in terms of classification of the family is the derivation of unisexual from bisexual flowers. Subfamilial classification in the family has been, in part, variously interpreted based on decisions concerning the evolution of unisexuality. As part of a longer term study of development in the Araceae with the goal of elucidating ontogenetic mechanisms responsible for generation of floral diversity, a study of floral development was undertaken in an array of species with unisexual flowers in the subfamily Aroideae (sensu latoMayo, Bogner and Boyce, 1997). Primary objectives of the study were to: 1) describe patterns of development of male, female and sterile flowers with particular reference to "transition" stages 2) compare patterns of development among genera with unisexual flowers to determine the commonality of ontogenetic mechanisms contirbuting to divergences in floral form. Emphasis in this paper is primarily focussed on a study of floral development inSyngonium podophyllum. Preserved shoot and floral material of this species was dissected and examined by SEM. Syngonium is monoecious producing a spadix with an apical zone of male flowers with stamens united in synandria, an intermediate zone of sterile flowers, and a small basal zone of female flowers with connate gynoecia. Patterns of development will be contrasted with those observed for Cercestis congensisand Peltandra virginica.

Key words: Araceae, classification, floral development, Syngonium, unisexuality