Patterns of long-distance dispersal in Tiquilia subg. Tiquilia (Boraginaceae):: implications for the origins of amphitropical disjuncts and Galapagos Islands endemics

Plant biogeographers have long argued whether plant disjunctions result from vicariance or dispersal. One of the classic patterns of plant disjunction involves New World amphitropical disjuncts, as exemplified by Tiquilia subg. Tiquilia (Boraginaceae). Subgenus Tiquilia forms a heterogeneous group of similar to 20 species that is amphitropically distributed in the deserts of North and South America, with four taxa endemic to the Galapagos Islands. The current study reconstructs the biogeographic history of subg. Tiquilia in order to explore the origins of New World amphitropical disjunction and of Galapagos endemism. A strongly supported phylogeny of the subgenus is estimated using sequence data from matK, ndhF, rps16, ITS, and waxy. Biogeographic analyses using combined and individual marker data sets reveal a complex history of long-distance dispersal in subg. Tiquilia. Biogeographic reconstructions imply a North American origin of the subgenus and its three major lineages and require at least four long-distance dispersal events to explain its current distribution. The South American taxa of subg. Tiquilia result from three independent and nonsimultaneous colonization events, while the monophyly and continental origins of the Galapagos endemics are unresolved. This study contributes to a growing body of evidence that intercontinental dispersal has been more common than previously realized.