Pleistocene radiation of coastal species of Pilosocereus (Cactaceae) in eastern Brazil

•Genetic gaps displayed by Pilosocereus catingicola populations agree with riverine boundaries.•Informal taxonomic groups of Pilosocereus do not form monophyletic clades.•Coastal species of Pilosocereus experienced Quaternary radiation.•Quaternary climate cycles affected Pilosocereus differently in NE and SE Brazil.•Hypothesis that Pilosocereus arrabidae group diverged early within the subgenus is refuted.

The semiarid region in Northeast Brazil (Caatinga) suffered several high moisture periods during the Pleistocene, while neighbouring regions experienced drying events. Effects of this climatic history on the evolution of Caatinga xeric flora are poorly understood. Demography and evolutionary relationships between Pilosocereus arrabidae and Pilosocereus catingicola (Cactaceae) were investigated using two non-coding intergenic spacers of cpDNA (1424 bp) employing distinct statistical methods, such as Bayesian Inference analysis, haplotype network, AMOVA, neutrality tests and Bayesian Skyline Plot. Our data suggests that species formerly arranged as the informal Pilosocereus arrabidae group do not form a monophyletic clade. P. arrabidae and P. catingicola are not reciprocally monophyletic and present very low genetic diversity. The Tajima's D and Fu's Fs statistics provided no significant results. Results suggest a very recent origin for P. arrabidae and P. catingicola. The beginning of P. arrabidae and P. catingicola diversification dates back to the Pleistocene. Genetic diversity of P. catingicola subsp. salvadorensis is geographically structured between major rivers of the region, suggesting a history of isolation in interfluves during Pleistocene climatic cycles.