Bioregionalisation of vascular aquatic macrophytes endemic to the Neotropical region.

The Neotropical region harbours the world’s highest diversity of endemic aquatic plants. Due to their diversity of lifeforms and dependency on aquatic environments for survival, these taxa may not exhibit a broad-scale biogeographic pattern consistent with hydrographic basins. Based on 90,409 occurrence records of 778 aquatic plant species endemic to the Neotropics, we delineated bioregions to evaluate regional connectivity and compared the resulting map with hydrographic basin boundaries. We then deployed spatial autoregressive models to test whether climatic heterogeneity (precipitation and temperature), topographic complexity, and paleoclimatic stability influenced bioregional boundaries. We identified 18 bioregions, whose limits did not coincide with hydrographic basins. Boundaries were instead linked to steep precipitation gradients and rugged terrain, highlighting their role as key drivers of Neotropical aquatic plant biogeography. Markov time analysis further identified the influence of physical barriers in driving bioregionalisation patterns. The mismatch between bioregions and river basins reflects distinct dispersal strategies and water dependency, underscoring the need for taxon-specific regionalisation. Phylogenetic inclusion confirmed that bioregions capture both taxonomic assemblages and evolutionary history, while rare-species weighting highlighted fine-scale areas as priorities for conservation. The integrative framework developed here advances our understanding of aquatic plant biogeography and provides valuable information to support wetland conservation.