Floral Ontogeny and Morphology in Subfamily Spiraeoideae Endl. (Rosaceae).

"Spiraeoideae," as traditionally circumscribed, contain the greatest diversity of floral organ morphology of any of the four subfamilies in the Rosaceae. Comparisons of mature floral morphology in 10 spiraeoid genera demonstrate that genera in this subfamily exhibit many floral character states present in the other three subfamilies. Inflorescence development, gynoecium initiation and development, ovule development and morphology, and obturator position all exhibit considerable variation in these taxa. Inflorescences vary from simple and racemose to multibranched and cymose. Gynoecial appendages can be initiated as independent primordia or from a shallow gynoecial ring primordium. Placentation occurs on the ventral margin of the ovary locule and includes apotropic ovules inserted near the base (Porteranthus and Vauquelinia), apotropic and pleurotropic ovules inserted the entire length or midway (Kageneckia and Physocarpus), and apically inserted epitropic ovules (Aruncus, Chamaebatiaria, Holodiscus, Lyonothamnus, Sorbaria, and Spiraea). Associated with the ovules of almost all genera is an obturator that may comprise cells of the funiculus or cells of both the funiculus and locule margin. These results corroborate those of other studies that suggest that the "Spiraeoideae" are an artificial, polyphyletic group.