The presence and structure of EFNs in Opuntia robusta had not been investigated. We used light, scanning-electron, and transmission-electron microscopy to examine morphology, anatomy, and ultrastructure of the secretory spines in areoles in female and hermaphrodite individuals of O. robusta. Young cladodes develop areoles with modified and secretory spines as EFNs only active during the early growth phase of female and hermaphrodite individuals. EFNs are non-vascularized structures, with no stomata, that consist of three distinct tissues: a basal meristematic tissue; a middle elongation region; and an apical secretory cone (asc) formed by large globular epidermal cells, of sac shape, containing nectar and medullar elongated cells. TEM observations indicated the presence of Golgi apparatus, vesicles and plastids in the medullar and sup-epidermal cells of the asc, transporting nectar to the epidermal secretory cells. The nectar is transported through plasmodesmata, and then stored on the asc cells, to be secreted by breaking through the globular cells and pores.