RESEARCH ARTICLE Munroa argentina, a Grass of the South American Transition Zone, Survived the Andean Uplift, Aridification and Glaciations of the Quaternary

The South American Transition Zone (SATZ) is a biogeographic area in which not only orog-eny (Andes uplift) and climate events (aridification) since the mid-Miocene, but also Quater-nary glaciation cycles had an important impact on the evolutionary history of the local flora. To study this effect, we selectedMunroa argentina, an annual grass distributed in the bio-geographic provinces of Puna, Prepuna and Monte. We collected 152 individuals from 20 localities throughout the species ’ range, ran genetic and demographic analyses, and applied ecological niche modeling. Phylogenetic and population genetic analyses based on cpDNA and AFLP data identified three phylogroups that correspond to the previously identi-fied subregions within the SATZ. Molecular dating suggests thatM. argentina has inhabited the SATZ since approximately 3.4 (4.2–1.2) Ma and paleomodels predict suitable climate in these areas during the Interglacial period and the Last Glacial Maximum. We conclude that the current distribution ofM. argentina resulted from the fragmentation of its once continu-ous range and that climate oscillations promoted ecological differences that favored isola-tion by creating habitat discontinuity