Morphological and ultrastructural studies of floral nectaries in Rhamnaceae

Abstract

Morphology, anatomy and ultrastructure of nectaries of 12 species belonging to five tribes of Rhamnaceae (Pomaderreae, Colletieae, Paliureae and Gouanieae of the Ziziphoids clade, and Rhamneae of the Rhamnoids clade) are studied by light and electron microscopy. Four types of nectaries are observed in this study. Species of the tribes Rhamneae, Gouanieae, Paliureae and Cryptandra tomentosa of the Pomaderreae tribe have annular nectaries. Siegfriedia darwinioides and Stenanthemun humile (Pomaderreae) show revolute nectaries, along with Colletia paradoxa and C. spinossisima (Colletieae). Retanilla patagonica and Kentrothamnus weddellianus (Colletieae) have indistinct and adpressed nectaries respectively. Nectar secretion occurs through modified nectary stomata in all species. Differences in the ultrastructure, mode of nectar secretion and position of the nectaries are discussed. According to the organelles found in nectary cells of all the species studied, granulocrine secretion is most likely to occur. Further research of these structures in more species of this family could help to establish nectary homologies.