Nectary microstructure and nectar production in two species of Cephalocereus (Cactaceae) and their natural hybrid

Variation in the quantity and quality of reward substances produced by flowers influences reproductive success in angiosperms. In this study, a comparative analysis of nectaries and nectar traits (volume, concentration and sugar composition) was performed on the hybrid Cephalocereus columna-trajani × C. tetetzo and its parental species to identify phenotypic variation that could affect reproductive success. The presence of nectarostomata and two types of nectary cells are significant, as well as the presence of xylem and phloem. Furthermore, possible interspecific differences in the amount of starch and mucilage may be relevant. Interspecific variation in nectar volume and concentration was found, with the hybrid exhibiting the highest concentration. All three taxa presented hexose-dominated nectar. In conclusion, C. columna-trajani × C. tetetzo, like its parental species has a functional and anatomically well-formed nectary. Differences in traits such as the amount of starch and mucilage associated with nectar volume, in combination with differences in nectar concentration could have potential consequences for fitness. Our results confirm previous reports on the development of functional structures in hybrid flowers and serve as the basis for future studies testing whether the differences observed here govern the dynamics of competition in hybridization zones.