Floral Organogenesis of Cocculus orbiculatus and Stephania dielsiana (Menispermaceae)

Floral ontogeny of two dioecious species in the Menispermaceae, Cocculus orbiculatus and Stephania dielsiana, was compared using scanning electron microscopy (SEM). In C. orbiculatus, flowers exhibit rudiments of a nonfunctional organ of the opposite sex. Female flowers have six stamens that remain primordial; however, male flowers usually have three carpellodes rather than six, and hence have a different number of carpels than female flowers. Development of carpellodes in the family was described under SEM for the first time. The male and female of C. orbiculatus are almost homomorphic in early developmental stages, with eight alternating whorls of four types of organs (sepals, petals, stamens/staminodes, and carpels/ carpellodes) arising centripetally. In S. dielsiana, no vestigial sexual organs were found, and the symmetry of male and female flowers differs, with males being actinomorphic and females zygomorphic. The six stamens of C. orbiculatus are free, whereas the three or four stamens of S. dielsiana are united congenitally. There are six carpels in females of C. orbiculatus but a single one in S. dielsiana. In overview, all flowers are actinomorphic and trimerous, with the female flower of S. dielsiana being the exception. This may be the result of reduction and is yet to be determined