How the temperate world was colonised by bindweeds: biogeography of the Convolvuleae (Convolvulaceae)

Background At a global scale, the temperate zone is highly fragmented both between and within hemispheres. This paper aims to investigate how the world’s disjunct temperate zones have been colonised by the pan-temperate plant group Convolvuleae, sampling 148 of the c . 225 known species. We specifically determine the number and timing of amphitropical and transoceanic disjunctions, investigate the extent to which disjunctions in Convolvuleae are spatio-temporally congruent with those in other temperate plant groups and determine the impact of long-distance dispersal events on diversification rates. Results Eight major disjunctions are observed in Convolvuleae: two Northern Hemisphere, two Southern Hemisphere and four amphitropical. Diversity in the Southern Hemisphere is largely the result of a single colonisation of Africa 3.1–6.4 Ma, and subsequent dispersals from Africa to both Australasia and South America. Speciation rates within this monophyletic, largely Southern Hemisphere group (1.38 species Myr −1 ) are found to be over twice those of the tribe as a whole (0.64 species Myr -1) . Increased speciation rates are also observed in Calystegia (1.65 species Myr −1 ). Conclusions The Convolvuleae has colonised every continent of the world with a temperate biome in c . 18 Myr and eight major range disjunctions underlie this broad distribution. In keeping with other temperate lineages exhibiting disjunct distributions, long-distance dispersal is inferred as the main process explaining the patterns observed although for one American-Eurasian disjunction we cannot exclude vicariance. The colonisation of the temperate zones of the three southern continents within the last c . 4 Myr is likely to have stimulated high rates of diversification recovered in this group, with lineage accumulation rates comparable to those reported for adaptive radiations.