Extrafloral Nectaries in Kudzu, Pueraria montana (Lour.) Merr., and Groundnut, Apios americana Medicus (Fabaceae)

The inflorescences of kudzu, Pueraria montana, and the groundnut, Apios americana, have extrafloral nectaries at the base of each multiple-flowered fascicle. In P. montana, the EFNs lie under the lateral flowers and appear to become active and accessible only when the covering flower abscises and drops. In A. americana, there is one EFN per fascicle, representing an aborted secondary short-shoot. Five species of ants were observed visiting P. montana EFNs and six species at A. americana EFNs (four of which were found on both). EFN-related behaviors varied among ant species, but not within ant species between plants. The location and timing of these heretofore overlooked EFNs suggests a role in protecting early developing seeds. Thus, the low seed set reported for P. montana in its introduced range on the one hand and for A. americana in cultivation on the other might be explained by a shortage of ant mutualists in these atypical situations.