Knowledge gaps in legume diversity and distribution and prospects for future research

Despite significant advancements in legume (Leguminosae or Fabaceae) taxonomy, biogeography and phylogenetics, substantial knowledge gaps persist, limiting our ability to understand their diversity, evolutionary history and conservation needs. In this study we used a robust taxonomic backbone and information housed in publicly available biodiversity repositories to quantify global knowledge gaps within the legume family, focusing on the completeness of species inventory (Linnean shortfall), geographic coverage (Wallacean shortfall), and evolutionary representation (Darwinian shortfall). Our findings underscore that approximately 11% of legume species are yet to be described, with high concentrations in regions such as Iran, Northwestern China, Western Australia, Cape Provinces, and Northeast Brazil. The assessment of gaps in geographic coverage revealed that around 19.8% of legume species lack any occurrence record in public databases. Additionally, nearly 50% of species had fewer than ten occurrence records, and another 50% had incomplete geographic coverage relative to their known distributions. Significant geographic gaps were identified in Temperate Asia, particularly Iran, Afghanistan, and Turkey. Furthermore, the limited availability of comprehensive DNA sequence data for key markers (ITS, matK, psbA, rbcL, trnL), with 52.5% of species lacking sequences for these markers, poses challenges for accurate phylogenetic inference, especially for clades from poorly sampled regions like South America and Temperate Asia. Addressing these gaps requires integrative approaches that combine herbarium collection assessments, targeted fieldwork, enhanced data integration across repositories, and advanced phylogenetic techniques. By prioritising these strategies, we can accelerate the pace of species discovery and refine biogeographical and phylogenetic understanding for this ecologically and economically important group of plants.