Do nectary morphology, anatomy, and nectar production differ between two Salvia taxa with contrasting floral traits and floral visitor assemblages?

Floral nectaries are specialized structures that secrete nectar, a key floral reward mediating plant-pollinator interactions. Although floral morphology and nectar traits have been moderately studied in Salvia, the detailed structure and anatomy of nectaries remain less explored, limiting our understanding of their diversity and functional variation. This study compares the nectary accessibility, morphology, anatomy, and nectar production of two Salvia taxa with different floral traits and floral visitor assemblages: S. uliginosa and the the sterile hybrid cultivar S. 'Amistad'. Both possess annular, four-lobed nectaries positioned below the ovary, with the anterior lobe being the most developed. However, S. 'Amistad' exhibits significantly larger nectaries and produces higher nectar volumes (16.85 ± 1.13 µL) than S. uliginosa (0.36 ± 0.03 µL), with nectary size, particularly anterior lobe length, associated with nectar production differences. Anatomically, both taxa show a single-layered epidermis with open nectarostomata and a nectariferous parenchyma well supplied by vascular bundles containing phloem and xylem. Epidermal micromorphology differs between species: the cuticle is smooth in S. uliginosa but striate in S. 'Amistad'. Although bees dominated floral visitation in both taxa, hummingbirds accounted for a substantial proportion of visits (35.1%) to S. 'Amistad' and were the only visitors contacting its reproductive structures, whereas only bees contacted the reproductive structures of S. uliginosa. Because S. 'Amistad' is a sterile cultivar, floral visitor observations are interpreted in the context of differences in nectar accessibility, nectar production, and floral visitor assemblages rather than as evidence of pollinator-mediated selection. These comparative data reveal conserved nectary anatomy with subtle structural variation associated with nectar production differences between two Salvia taxa with contrasting visitor assemblages.