Four New Pinnularia Ehrenberg Species (Bacillariophyta) from Urban Freshwater Streams in South Korea

This study reports the discovery of four novel <i>Pinnularia</i> species-<i>P. latocentra</i> sp. nov., <i>P. rhombocentra</i> sp. nov., <i>P. seouloflexuosa</i> sp. nov., and <i>P. paristriata</i> sp. nov.-from urban freshwater streams in South Korea. Species delimitation was achieved using a polyphasic approach that integrated light and scanning electron microscopy, ecological profiling, and molecular evidence from SSU rRNA and <i>rbcL</i> sequences. Each taxon was confirmed as morphologically and genetically distinct from its closest congeners. Our findings broaden the recognized diversity of <i>Pinnularia</i> in East Asia and demonstrate that urban streams, often regarded as degraded habitats, can harbor hidden diatom diversity and ecological complexity. By clarifying diagnostic traits, validating type material in a recognized repository, and aligning molecular and morphological evidence, this study contributes to a more robust taxonomy of <i>Pinnularia</i>. These results also highlight the importance of polyphasic taxonomy and the strategic inclusion of urban habitats in diatomological surveys and biodiversity assessments.