Mapping the research landscape of extrafloral nectaries: a comprehensive bibliometric analysis (1894-2026)

Extrafloral nectaries (EFNs) are nectar-secreting glands on vegetative organs that mediate indirect plant defense by recruiting predatory arthropods. Documented in over 4,999 species across 129 families, with at least 457 independent evolutionary origins, they are the intersection of anatomy, chemical ecology, entomology, and evolutionary biology, yet no study has systematically mapped the bibliometric structure of this field. To the best of our knowledge, we present the first comprehensive science-mapping analysis of global EFN research. Bibliographic records were retrieved from Scopus and the Web of Science Core Collection, then merged, deduplicated, and screened in accordance with PRISMA 2020 guidelines adapted for bibliometric research. Quantitative analyses were performed using the R package bibliometrix (v5.2.1) and VOSviewer (v1.6.20). The final dataset comprised 1,279 publications (1894-2026) across 343 sources by 2,660 authors. A logistic growth model (R² = 0.938) indicated the field has reached approximately 87.6% of projected maturity, with peak growth around 2016. Brazil, the USA, and Mexico led corresponding-author output (44.5% combined), while African contributions remained marginal and Japanese and Indian contributions were substantial but internationally isolated. Oecologia headed fourteen core journals under Bradford's Law, and Del-Claro K was the most prolific author. Walktrap clustering identified five thematic clusters: nectary anatomy/chemistry, EFN-ant ecological networks, biological control, mutualism-herbivory-indirect defense, and nectary ultrastructure. Thematic evolution traced an arc from morphological description through ecological experimentation to network-level analysis, with climate change emerging as a distinct theme in the most recent period (median keyword year: 2021). The biological control cluster remained the smallest and most isolated, despite demonstrated agricultural applications. International collaboration was concentrated along the Brazil-USA and Brazil-Mexico corridors across 262 bilateral links. These results provide a quantitative foundation for identifying knowledge gaps, particularly the underrepresentation of African and Asian research communities, the nascent climate-change frontier, and the disconnect between fundamental EFN ecology and applied pest management.