Floral ontogeny and morphology in subfamily Spiraeoideae endl. (Rosaceae)

"Spiraeoideae," as traditionally circumscribed, contain the greatest divers ity of floral organ morphology of any of the four subfamilies in the Rosace ae. Comparisons of mature floral morphology in 10 spiraeoid genera demonstr ate that genera in this subfamily exhibit many floral character states pres ent in the other three subfamilies. Inflorescence development, gynoecium in itiation and development, ovule development and morphology, and obturator p osition all exhibit considerable variation in these taxa. Inflorescences va ry from simple and racemose to multibranched and cymose. Gynoecial appendag es can be initiated as independent primordia or from a shallow gynoecial ri ng primordium. Placentation occurs on the ventral margin of the ovary locul e and includes apotropic ovules inserted near the base (Porteranthus and Va uquelinia), apotropic and pleurotropic ovules inserted the entire length or midway (Kageneckia and Physocarpus), and apically inserted epitropic ovule s (Aruncus, Chamaebatiaria, Holodiscus, Lyonothamnus, Soubaria, 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.