New molecular evidence for Canarian endemic Ruta (Rutaceae: Ruteae) reveals a complex evolutionary history and overlooked diversification processes

We studied four currently recognized endemics of Ruta (Rutaceae) from the Canary Islands, an oceanic biodiversity hotspot, to identify genetic variation, reconstruct evolutionary relationships and clarify the taxonomic delimitation of several recently discovered populations. We analysed four plastid DNA regions for a thorough population sampling of Ruta oreojasme on Gran Canaria, R. pinnata on Tenerife and La Palma and R. microcarpa and the only known population of the recently described R. nanocarpa on La Gomera. Bayesian clock dating analysis, haplotype network and ancestral area reconstructions were carried out. Our results reveal a complex, extremely dynamic and largely overlooked pattern of colonization and evolutionary history of Ruta in the archipelago. Thirty haplotypes were found, but only one of them was shared across more than one island. Species divergence and all colonization events in the Canary Islands were dated from the late Pliocene to the Pleistocene, and R. oreojasme has an earlier origin than its Canarian congeners. Multiple secondary colonization events between and within islands account for the diversification of R. pinnata and R. microcarpa. Our data cannot discard a possible independent origin of R. oreojasme and do not support the currently accepted circumscription of R. pinnata and R. microcarpa. Rather, the high levels of genetic differentiation detected suggest the existence of ongoing diversification processes and of new taxa. Urgent population-level conservation efforts should be undertaken, especially focused on the single population on La Gomera that can be attributed to R. microcarpa, R. nanocarpa and genetically distinct populations from La Palma and the palaeo-islands of Tenerife.