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Summary The genusDelphiniumexemplifies the complexity of plant diversification in mountainous regions, where rapid speciation, hybridization, and morphological convergence frequently obscure species boundaries. The North American lineageDelphiniumsect.Diedropetalahas rapidly radiated across a range of ecological habitats, from alpine tundra to desert grasslands, forming an iconic component of western wild flower communities.Here, we present a genome‐scale phylogeny of 34 taxa using ddRAD‐seq data from 150 individuals sampled across their geographic ranges.Our results reveal strong phylogenetic structure corresponding to biogeographic regions, including several well‐supported clades that cut across existing taxonomic subsections, emphasizing the need for taxonomic revision. Hybridization and introgression are widespread, occurring both within and between these regional clades. Most species are connected through a syngameon‐like network of introgression, with few widespread species acting as central hubs. We describe six higher‐level clade names and use an agent‐based artificial intelligence analysis to identify morphological synapomorphies that align with our genomic findings.Our study demonstrates that geography and gene flow have played a dominant role in shaping the evolutionary history ofDelphiniumin North America, offering a framework for revising its taxonomy and informing future conservation efforts. 

Here we use population genomic data (ddRAD-Seq) and ecological niche modeling to test biogeographic hypotheses for the divergence of the island-endemic cactus species Cereus insularis Hemsl. (Cereeae; Cactaceae) from its sister species C. fernambucensis Lem. The Cereus insularis grows in the Fernando de Noronha Islands (FNI), a Neotropical archipelago located 350 km off the Brazilian Atlantic Forest (BAF) coast. Phylogeographic reconstructions support a northward expansion by the common ancestor of C. insularis and C. fernambucensis along the mainland BAF coast, with C. insularis diverging from the widespread mainland taxon C. fernambucensis after colonizing FNI in the late Pleistocene. The morphologically distinct C. insularis is monophyletic and nested within C. fernambucensis, as expected from a progenitor-derivative speciation model. We tested alternative biogeographic and demographic hypotheses for the colonization of the FNI using Approximate Bayesian Computation. We found the greatest support for a stepping-stone path that emerged during periods of decreased sea level (the “bridge” hypothesis), in congruence with historical ecological niche modeling that shows highly suitable habitats on stepping-stone islands during glacial periods. The outlier analyses reveal signatures of selection in C. insularis, suggesting a putative role of adaptation driving rapid anagenic differentiation of this species in FNI.