A revised phylogeny and taxonomy of Buckleya (Thesiaceae)

Abstract Buckleya is a small genus in Thesiaceae, sometimes merged into the broadly circumscribed Santalaceae sensu lato (not adopted in this study), with five currently recognized hemiparasitic species and a distinct East Asian–North American disjunct distribution. However, its taxonomy is still controversial on certain taxa and its diversification history as well as future evolutionary trends have not been comprehensively investigated. This study includes 21 samples representing all currently recognized 5 Buckleya species, supplemented by 29 Santalaceae s.l. plastid genomes and 27 Santalaceae s.l. 353‐gene sets obtained from public databases for phylogenetic analysis. Additionally, morphological and distribution data from 286 specimens including all 5 Buckleya species were compiled for morphological and ecological investigations. Buckleya is monophyletic, and is sister to Thesium , belonging to Thesiaceae. Widespread loss ( ndhA , ndhC , ndhE , ndhF , ndhG , ndhI , ndhJ , ndhK ) or pseudogenization ( ndhD , ndhH ) of the NDH family was observed in chloroplast genomes of Buckleya . Combining evidence from morphology and phylogeny, this study recognizes four species, treating B. angulosa as a new synonym of B. henryi , and resolves long‐standing taxonomic confusion between B. henryi and B. lanceolata . More analyses revealed that Buckleya originated in the early Miocene and later species divergence is found to be primarily driven by precipitation patterns, and divergence events correspond well to historical climatic changes and geographical isolation. Under future climate change, species responses are projected to vary among congeners: some species, such as B. distichophylla , are expected to expand their suitable habitats, whereas others, including B. graebneriana , may experience significant contraction, suggesting that conservation strategies should prioritize ecological corridors connecting current and future suitable habitats to enhance climate resilience. This study highlights the value of integrating multiple lines of evidence to resolve taxonomic disputes, and combining diversification history with future projections to further elucidate the evolutionary processes of taxa.