Organogenèse de la fleur pistillée du Begonia horticola (Begoniaceae)

Abstract

The placentation of the inferior ovary of the female flower of Begonia horticola Irmscher (section Tetraphila) is mostly axile with the upper part parietal. A study of the vascular organisation and of the organogenesis of this species allows us to better understand the transition from axile to parietal placentation observed in other Begoniaceae, from both morphological and evolutionary points of view. The anatomy of the mature female flower is similar to that of other Begonia species. Anatomical sections and scanning electron microscopy of young developmental stages show that the inferior ovary grows underneath the perianth primordia. The two types of placentation are established early. The axile part develops from an axial meristem, while the parietal placentas are formed by the development of septa towards the inside of the cavity. It is however impossible to draw a clear boundary between the two tissues. The present data do not allow us to infer the evolutionary status of placentation types in Begonia.