Print PageExtrafloral nectaries (EFNs) are plant glands that secrete sugar water and are located outside the flower. Most studies of EFN function support their role in defense, as they attract invertebrate predators whose presence can reduce herbivory. We summarize the taxonomic distribution of EFNs using a compilation of publication records for plants reported as having EFNs in the literature over the last 139 years. Using comparisons of parametric and non-parametric models, we estimate the number of unreported cases of EFN likely to exist beyond the publication list. Finally, we place this information into a phylogenetic context using broadly sampled mega-trees of seed plant families.
Results/Conclusions
Analyses suggest that EFNs have been reported in over 4,000 species representing 750 genera in 117 families, about ~1.9% of vascular plants. They are found in all major orders of angiosperms, as well as in three fern families, but are absent in Gymnosperms. EFNs are irregularly scattered throughout Angiosperm orders, are unknown in basal Angiosperms and Magnoliid families, but are common throughout monocotyledons, including a few grasses, various Liliaceae (sensu latu), and frequently occur on the pedicels and peduncles of orchids. Many advanced Eudicots have EFNs, including species within the Asterales, Lamiales and Gentianales although EFNs have not been reported in the Apiales. Phylogenetic analyses based on our current knowledge strongly support the repeated gain and loss of EFN across plant clades, especially in more derived dicot families, and suggest that at a minimum or 74 gains and 5 losses are necessary to explain their distribution. However, model selection methods estimate that the number of unreported cases of EFNs may be as high as the number of species already reported, and thus more fine scale surveys of EFNs in major plant groups are ultimately needed to better understand these patterns.
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