Integrative Taxonomic Reappraisal and Molecular Phylogeny of Freshwater Mussels of the Genus <i>Lanceolaria</i> (Bivalvia: Unionidae), With Description of Two New Species

ABSTRACT Effective species conservation requires accurate identification of target taxa; however, the large intraspecific variation and strong phenotypic plasticity of shell morphology in freshwater mussels (Bivalvia: Unionidae) exacerbate taxonomic uncertainties, thereby complicating species delineation. Based on extensive geographic sampling, we conducted an integrative taxonomic revision and phylogenetic reconstruction of the freshwater mussel genus Lanceolaria by integrating shell morphology, geometric morphometrics, sequence data from multiple gene loci ( COI , 16S rRNA, 18S rRNA and 28S rRNA) and mitogenome datasets. Molecular species delimitation methods and Fourier morphometric analysis confirmed two new species: Lanceolaria danzhouensis sp. nov., distributed in southern China and Vietnam and closely related to Lanceolaria grayii ; and Lanceolaria helianthoides sp. nov., from Guangdong Province, China, which is closely related to Lanceolaria lanceolata . Additionally, we recognized Lanceolaria cylindrica syn. nov., Lanceolaria eucylindrica syn. nov. and Lanceolaria yueyingae syn. nov. as junior synonyms of Lanceolaria grayii , and the species exhibited extremely strong environmental adaptability and phenotypic plasticity. We first sequenced the mitochondrial genomes of five species within the genus. Based on multilocus and mitogenomic phylogenetic analyses, our results elucidated intrageneric relationships and revealed three major clades. Overall, we clarified the classification of the genus Lanceolaria , resolved long‐standing taxonomic disputes, evaluated its species diversity and provided a reliable phylogenetic and taxonomic framework for this genus.