Floral nectar is a sugar-rich liquid generated by plants to attract pollinators. The critical components of nectar are sugars in varying concentrations and forms, yet many also include a range of phytochemicals that attract pollinators and deter predators1. These compounds include alkaloids, flavonoids, terpenes, and others, which have been found to affect pollinator behavior and influence their preference for the nectar. Colored nectar is a distinctive and uncommon trait of nectar. While scientists have known about colored nectar since at least 1785, it has only lately gained concerted scientific investigation2. Melianthus species produce black nectar that is believed to attract avian pollinators visually; however, the chemical identity and synthesis of the black pigment are unknown2,3. To identify the pigment responsible for the black color of Melianthus nectar and its biosynthesis mechanism, a combination of analytical biochemistry, transcriptomics, proteomics, and enzyme assays were utilized. Here, we demonstrate that the black nectar produced during anthesis contains a natural analog of iron-gall ink formed from an ellagic acid-Fe complex4. High concentrations of ellagic acid and iron give the nectar its dark black color, which may be replicated using synthetic solutions containing solely ellagic acid and iron (III). The nectar also includes a peroxidase, which oxidizes gallic acid to generate ellagic acid. In vitro processes, including nectar peroxidase, gallic acid, hydrogen peroxide, and iron (III), completely replicate the black color of the nectar. The use of visual modeling of pollinators was further employed to deduce the probable function of the black coloration. Results indicate that within the context of the flower, the black nectar is conspicuous to avian pollinators5. While this study focused on the impact of black nectar as a visual cue to pollinators, it may also serve other non-exclusive functions. As the pH and polyphenol content of nectar vary with the flowering stage, stage-specific filtering of floral visitors may occur6. Comparing Melianthus nectar to dark-colored nectars from Schiedea, Leucosceptrum, and Aloe species may help explain how chemistry and color influence fitness6–8.