Floral Ontogeny and Morphology in Subfamily Amygdaloideae T. & G. (Rosaceae).

Relationships within the Amygdaloideae have long been a point of discussion in Rosaceae systematics. Oemleria, a monotypic genus, has been removed from the Amygdaloideae because of its five-pistillate gynoecium since all other genera have a single pistil. Exochorda, with its capsular fruit, has traditionally been placed in Spiraeoideae. Nevertheless, recent phylogenetic analyses of wood anatomy and rbcL sequence variation have demonstrated that both Exochorda and Oemleria should be included in an expanded Amygdaloideae. Comparisons of floral ontogeny in Prunus, Oemleria, and Exochorda, and the mature morphology of these genera and Prinsepia, support inclusion of Oemleria and Exochorda in Amygdaloideae. Inflorescence development demonstrates a close relationship between Exochorda and Oemleria. Gynoecium development in Exochorda and Oemleria is similar in some ways to that of some members of the Maloideae. All genera have a pair of collateral, bitegmic ovules, each of which is associated with an obturator that is composed of cells of the ventral margin of the locule.