title: The diversity, ecology and evolution of extrafloral nectaries: current perspectives and future challenges.
abstract: BACKGROUND
  Plants in over one hundred families in habitats worldwide bear extrafloral nectaries (EFNs). EFNs display a remarkable diversity of evolutionary origins, as well as diverse morphology and location on the plant. They secrete extrafloral nectar, a carbohydrate-rich food that attracts ants and other arthropods, many of which protect the plant in return. By fostering ecologically important protective mutualisms, EFNs play a significant role in structuring both plant and animal communities. And yet researchers are only now beginning to appreciate their importance and the range of ecological, evolutionary and morphological diversity that EFNs exhibit.
  
  
  METHODS
  This Highlight features a series of papers that illustrate some of the newest directions in the study of EFNs. Here, we introduce this set of papers by providing an overview of current understanding and new insights on EFN diversity, ecology and evolution. We highlight major gaps in our current knowledge, and outline future research directions.
  
  
  CONCLUSIONS
  Our understanding of the roles EFNs play in plant biology is being revolutionized with the use of new tools from developmental biology and genomics, new modes of analysis allowing hypothesis-testing in large-scale phylogenetic frameworks, and new levels of inquiry extending to community-scale interaction networks. But many central questions remain unanswered; indeed, many have not yet been asked. Thus, the EFN puzzle remains an intriguing challenge for the future.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA. marazzibrigitte@gmail.com
authors.forename: Brigitte
authors.initials: B
authors.lastname: Marazzi
authors.forename: Judith L
authors.initials: JL
authors.lastname: Bronstein
authors.forename: Suzanne
authors.initials: S
authors.lastname: Koptur
mesh_terms: D000818:Animals; D001000:Ants; D005075:Biological Evolution; D057048:Plant Nectar / Q000378:metabolism; D010944:Plants / Q000033:anatomy & histology*; D013559:Symbiosis
chemical_list: D057048:Plant Nectar
keywords: Angiosperms; ants; ant–plant interactions; extrafloarl nectaries; extranuptial; extrasoral; ferns; herbivory; interaction networks; mutualisms; nectar; plant defence; protection