Phylogeny and Biogeography of Acaena (Rosaceae): Evidence of Multiple Long-Distance Dispersal Events in the Southern Hemisphere

Although the species of Acaena Mutis ex L. (Rosaceae) have been the subjects of several taxonomic treatments, to date, no phylogenetic study has included sampling most of the species around the world (45 species). Acaena is the largest and most variable genus within the tribe Sanguisorbeae; however, all species have a conspicuous and distinctive hypanthium, which is commonly armed with hooked prickles.;Acaena, a predominantly Southern Hemisphere genus, presents two cases of disjunct distribution: a Gondwanan distribution among Southern Hemisphere landmasses and an Amphitropical distribution between North America and South America.;The current study was conducted to elucidate the phylogenetic relationships and biogeographic patterns in Acaena. Phylogenetic analyses of non-coding nuclear (ITS region) and chloroplast (trnL-F) markers using maximum parsimony, maximum likelihood and Bayesian analyses confirm the results of previous studies in showing that Acaena is a paraphyletic group with Margycarpus sp. and Tetraglochin sp. nested within it. The combined dataset provide better resolution among the clades and their species composition, compared to analyzing the nuclear or chloroplast regions independently. Nevertheless, many clades are weakly supported, which may be due to rapid radiations and lack of informative characters for markers used.;The most widespread and variable species in the genus is A. magellanica. The evolutionary relationships among multiple individuals of A. magellanica (20 accessions) indicate that five individuals present genetic variation and each can be treated as a separate variety or species.;We propose that both types of disjunct distributions are explained primarily by long-distance dispersal. Our results suggest the genus originated in South Africa, followed by migration into South America and colonization of the temperate regions of Chile and Argentina. Our results show that the main sources of dispersal events as well as the center of diversity for the genus are located in Chile and New Zealand.;The current distribution in the Southern Hemisphere landmasses can be explained mainly by two dispersal events, first, from Chile to New Zealand, and second, from New Zealand to Chile. Of the species from the Northern Hemisphere, those located in California and Hawai'i have different origins. New Zealand species contributed to the origin of Hawaiian species, while the Californian species originated from Chilean species.;The evolutionary relationships of species in Acaena combine a history of rapid radiations, long-distance dispersal and genetic variation within particular taxa. Further research should be undertaken to clarify the infraspecific classification of A. magellanica..