Explaining disjunct distributions in the flora of southern South America: evolutionary history and biogeography of Myrceugenia (Myrtaceae)

Aim Past climatic and geological events can be used to interpret present distributions of organisms. We use chronological and spatial analyses of the species of Myrceugenia in southern South America to help explain their present distribution. Location Southern South America (Argentina, Brazil, Chile, Paraguay and Uruguay). Methods Chronological analyses were completed for the tribe Myrteae (Myrtaceae) using two nuclear DNA sequences and for the genus Myrceugenia using four chloroplast and two nuclear sequences. A biogeographical analysis of Myrceugenia was carried out. Based on calibration points from fossils and estimations, a relaxed molecular clock was used to estimate divergence times and rates of speciation within each lineage. Ancestral states were reconstructed through Bayesian analysis. Results The chronogram implies that tribe Myrteae diversified at the end of the Cretaceous, but that the majority of the individual lineages originated more recently. Myrceugenia diverged into four lineages during the early Miocene. Three of these lineages diversified in Chile, with dispersal to the north and south of the country plus a recent dispersal to the Juan Fernandez archipelago. The fourth lineage diversified through vicariant events in south-eastern Brazil. The ancestors of Blepharocalyx, Myrceugenia fernandeziana and Luma are very ancient lineages that originated between the Palaeocene and Eocene, and which have remained stable with little or no subsequent diversification. Main conclusions The estimated age for diversification of tribe Myrteae is consistent with the known fossil evidence from southern South America. The distribution of Myrceugenia may be explained by a combination of three events occurring in the early-middle Miocene: uplift of the Andes, a rain-shadow effect and a marine transgression. These events may also have led to disjunct distributions in several other genera in southern South America.