Multiple windows of colonization to Macaronesia by the dispersal-unspecialized Scrophularia since the Late Miocene

Biogeographic hypotheses for the flora of Macaronesia have been subject of numerous studies given the singularity of a complex system of Atlantic volcanic islands. Phylogenetic analyses, divergence time estimates and biogeographic reconstructions of 10 Scrophularia species and subspecies distributed in Macaronesia and adjacent regions have been conducted in order to investigate the spatio-temporal patterns of island colonization. The Colonization Window Hypothesis (CWH) and the Relictual Series Hypothesis (RSH) proposed by previous authors were tested. Species and lineages relationships were analyzed based on one nuclear (ITS) and three plastid (trnL-trnF, psbA-trnH, trnQ-rps16) DNA regions, and using Bayesian inference and maximum likelihood methods. Biogeographic reconstructions were performed using specific maximum-likelihood (DEC) and parsimony-based (S-DIVA) methods. Our results supported at least five independent colonization events from the W Mediterranean to Macaronesian archipelagos by Scrophularia lineages. These events were the result of long-distance dispersal over sea barriers despite the unspecialized diaspores of Scrophularia. In addition, the colonization history of Macaronesian lineages of Scrophularia is better explained by the Colonization Window Hypothesis based on the geographical proximity of Macaronesian-W Mediterranean sister groups and the wide range of colonization times.