A tale of N orth and S outh A merica: time and mode of dispersal of the amphitropical genus M unroa ( P oaceae, C hloridoideae)

Plant disjunctions have provided some of the most intriguing distribution patterns historically addressed by biogeographers. We evaluated the three hypotheses that have been postulated to explain these patterns [vicariance, stepping‐stone dispersal and long‐distance dispersal ( LDD )] using M unroa , an A merican genus of grasses with six species and a disjunct distribution between the desert regions of N orth and S outh A merica. The ages of clades, cytology, ancestral characters and areas of distribution were investigated in order to establish relationships among species, to determine the time of divergence of the genus and its main lineages, and to understand further the biogeographical and evolutionary history of this genus. B ayesian inference recovered the N orth A merican M . pulchella as sister species to the rest. Molecular dating and ancestral area analyses suggest that M unroa originated in N orth A merica in the late M iocene– P liocene (7.2 Mya; 8.2–6.5 Mya). Based on these results, we postulate that two dispersal events modelled the current distribution patterns of M unroa : the first from N orth to S outh A merica (7.2 Mya; 8.2–6.5 Mya) and the second (1.8 Mya; 2–0.8 Mya) from S outh to N orth A merica. Arid conditions of the late M iocene– P liocene in the N eogene and Q uaternary climatic oscillations in N orth A merica and S outh A merica were probably advantageous for the establishment of populations of M unroa . We did not find any relationship between ploidy and dispersal events, and our ancestral character analyses suggest that shifts associated with dispersal and seedling establishment, such as habit, reproductive system, disarticulation of rachilla, and shape and texture of the glume, have been important in these species reaching new areas. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society , 2015, 179 , 110–125.