Continental diatoms (Bacillariophyta) from Paraná state, Brazil: a critical, georeferenced checklist and spatial synthesis

Abstract Freshwater diatom diversity remains unevenly documented across the Neotropics, limiting assessments of regional biodiversity and biogeographic patterns. We provide a critical, georeferenced synthesis of continental diatoms from Paraná State, southern Brazil, integrating bibliographic records, herbarium collections, nomenclatural revision, and spatial analyses. The compiled dataset comprises 86,775 occurrence records from 3649 samples collected between 1951 and 2025 at 712 georeferenced sites. After taxonomic and nomenclatural updates, 1525 accepted infrageneric taxa belonging to 190 genera, 71 families, and 35 orders were recognized. However, sampling was strongly spatially biased: Only 11.1% of the state territory was represented by Ottobasins containing confirmed records, and 258 of 399 municipalities lacked documented occurrences. Rarefaction and extrapolation analyses revealed pronounced differences in sampling completeness among hydrographic units, with several poorly sampled basins showing substantial discrepancies between observed and estimated richness. Approximately one quarter of all taxa were recorded from a single sampling locality, a pattern that, combined with the extensive spatial gaps in sampling, indicates that the geographic distributions of many taxa remain poorly characterized. Our synthesis demonstrates that Paraná harbors exceptionally high continental diatom diversity while substantial Linnean and Wallacean shortfalls persist, providing a spatially explicit framework for directing future inventories, biogeographic studies, and freshwater biomonitoring.