Herbivory has been a major selection force over plant evolution. This co-evolutionary arms race has led to a variety of plant defense mechanisms. One of particular interest is the presence of nectar-producing glands, which attract predatory ants that defend against herbivorous insects. While commonly studied in flowering plants, nectaries also occur on ferns—a group hypothesized to have minimal biotic interactions. Using a cross-kingdom phylogenetic-based approach we reveal three major insights on the evolution of nectaries in non-flowering plants: 1. fern nectaries evolved independently in at least seven lineages of ferns; 2. the potential to develop nectaries in the common ancestor of these lineages occurred during the Cretaceous, mirroring the diversification of ants associated with plants and the origin of extrafloral nectaries in flowering plants; and 3. a lag of almost 50 million years in the diversification of nectary-bearing ferns was likely driven by the Cenozoic rise of fern herbivores. This work represents a significant step towards understanding the evolution of nectaries, shedding new light on the intricacies of biotic interactions in ferns.