Complex evolution and biogeographic history of moss‐inhabiting flea beetles from the <scp>T</scp> aiwan‐ <scp>R</scp> yukyu <scp>I</scp> sland <scp>A</scp> rc ( <scp>C</scp> oleoptera: <scp>C</scp> hrysomelidae: <scp>A</scp> lticini)

Abstract Flightless insects distributed on islands are often characterized by dynamic evolutionary patterns, high endemism, and complex biogeographic histories, imposing challenges for integrative systematics. In this study, we explore the evolutionary history and biogeography of moss‐inhabiting flea beetles from the genus Ivalia in the Taiwan‐Ryukyu archipelago. Using phylogenomic data from 1649 ddRAD‐sequenced nuclear loci with 50,461 single‐nucleotide polymorphisms, we uncovered a complex biogeographic history shaped by Late Miocene vicariance and subsequent Pliocene dispersal events from Taiwan. Our results suggest that Ivalia populations on Amamioshima and Taiwan originated through vicariance from a Miocene continental ancestor, whereas other Ryukyu populations represent more recent colonizations from Taiwan. Within Taiwan, we identify an extensive species radiation – the Ivalia uenoi complex – characterized by high species diversity and endemism. Within this complex, we found striking mitonuclear discordance, likely driven by repeated mitochondrial introgression. This discordance led to erroneous species delimitations based on mitochondrial DNA barcoding. In contrast, species delimitation based on nuclear markers was congruent with putative species assignments based on rough morphological examinations. Moreover, we found signs of nuclear introgression events in the ancient history of the Taiwanese Ivalia . Our findings highlight Ivalia as a compelling case of island radiation shaped by dynamic evolutionary processes and underscore the critical role of integrative taxonomic frameworks in insect systematics.