Molecular phylogenetic evidence for the geographic origin and classification of Canary Island Lotus (Fabaceae: Loteae)

Abstract

Molecular phylogenetic analyses of Macaronesian Lotus and related genera were conducted to assess their biogeographic history and taxonomy. Macaronesian Lotus, which are typically classified within one of two subgenera, Lotus subgenus Pedrosia or L. subg. Rhyncholotus, are diagnosed by the presence of a forked or toothed style and differences in corolla morphology. Maximum parsimony and Bayesian analyses of internal transcribed spacer sequences identify a well-supported northwest African-Cape Verde Island clade that includes all members of Lotus subgenus Pedrosia+L. subg. Rhyncholotus. There is modest support for two independently nested clades containing the Canary Island species and two non-Canarian species, Lotus assakensis from Africa and Lotus azoricus endemic to the Azores. Biogeographic reconstruction based on a parsimony topology unequivocally identifies an African origin for the Canary Island group with subsequent back dispersal to the African continent and a single dispersal event to the Azores. A phylogeographic assessment of colonization and diversification patterns suggests that geographic isolation via interisland colonization of ecologically similar habitats is the primary mode of species diversification in Canary Island Lotus.