High tropical mountains harbour remarkable and fragmented biodiversity thought to a large degree to have been shaped by multiple dispersals of cold-adapted lineages from remote areas. Few dated phylogenetic/phylogeographic analyses are however available. Here, we address the hypotheses that the sub-Saharan African sweet vernal grasses have a dual colonization history and that lineages of independent origins have established secondary contact. We carried out rangewide sampling across the eastern African high mountains, inferred dated phylogenies from nuclear ribosomal and plastid DNA using Bayesian methods, and performed flow cytometry and AFLP (amplified fragment length polymorphism) analyses. We inferred a single Late Pliocene western Eurasian origin of the eastern African taxa, whose high-ploid populations in one mountain group formed a distinct phylogeographic group and carried plastids that diverged from those of the currently allopatric southern African lineage in the Mid- to Late Pleistocene. We show that Anthoxanthum has an intriguing history in sub-Saharan Africa, including Late Pliocene colonization from southeast and north, followed by secondary contact, hybridization, allopolyploidization and local extinction during one of the last glacial cycles. Our results add to a growing body of evidence showing that isolated tropical high mountain habitats have a dynamic recent history involving niche conservatism and recruitment from remote sources, repeated dispersals, diversification, hybridization and local extinction.

Department of Flow Cytometry Institute of Botany Průhonice Czech Republic

Department of Plant Biology and Biodiversity Management Addis Ababa University Addis Ababa Ethiopia

Natural History Museum University of Oslo Oslo Norway

Natural History Museum University of Oslo Oslo Norway CICA Centro de Investigacións Científicas Avanzadas Universidade da Coruña Galicia Spain

Natural History Museum University of Oslo Oslo Norway Department of Forest Biology Sokoine University of Agriculture Morogoro Tanzania

Natural History Museum University of Oslo Oslo Norway Department of Plant Biology and Biodiversity Management Addis Ababa University Addis Ababa Ethiopia

Natural History Museum University of Oslo Oslo Norway National Museums of Kenya Nairobi Kenya

School of Forestry Geographical and Environmental Sciences Department of Forestry Biodiversity and Tourism Makerere University Kampala Uganda

School of Forestry Geographical and Environmental Sciences Department of Forestry Biodiversity and Tourism Makerere University Kampala Uganda Natural History Museum University of Oslo Oslo Norway

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