Format: ORAL

1Carme Blanco-Gavald, 1Cristina Roquet, 1Gens Puig-Surroca, 2Santiago Andrs-Snchez,3 Sylvain G. Razafimandimbison, 4Rokiman Letsara, 5Nicola Bergh, 6Glynis V. Cron, 7Luca D. Moreyra, 8Juan Antonio Calleja, 1scar Castillo,9 Randall J. Bayer, 10Frederik Leliaert, 7Alfonso Susanna, 1Merc Galbany-Casals.

1 Systematics and Evolution of Vascular Plants (UAB) – Associated Unit to CSIC by IBB, Bellaterra, Spain. 2 University of Salamanca, Salamanca, Spain. 3 Swedish Museum of Natural History, Stockholm, Sweden. 4 Herbarium of the Parc Botanique et Zoologique of Tsimbazaza (PBZT), Antananarivo, Madagascar. 5 South African National Biodiversity Institute, Claremont, South Africa. 6 University of Witwatersrand, Johannesburg, South Africa. 7 Botanical Institute of Barcelona, Barcelona, Spain. 8 Autonomous University of Madrid, Madrid, Spain. 9 University of Memphis, Memphis, USA. 10 Meise Botanic Garden, Meise, Belgium.

Madagascar is a worlds biodiversity hotspot, showing exceptionally high levels of species richness and endemism. Despite the islands prolonged geographic isolation (150 to 160 Ma from Africa, 84 to 90 Mya from India), most of its extant endemic plant species are the result of recent long-distance dispersals, mainly from continental Africa. The genus Helichrysum is a relevant study-case to explore the evolutionary and biogeographic history of Malagasy flora because it represents one-fifth of the Compositae species of the island. We generated a time-calibrated phylogeny of 350 Helichrysum species (including 60% of the Malagasy endemics) based on target-enrichment DNA sequence data and conducted ancestral range estimation analyses. Our results reveal at least six independent dispersal events to Madagascar from African regions since the Pliocene. Notably, Madagascar was colonized at least twice by lineages originating from the Tropical Afromontane region, leading to significant subsequent radiations in the islands highlands and mountains. The southern African montane grasslands have also played a key role in Madagascars colonization, originating at least three clades on the island, one of which notably diversified. Helichrysum mahafaly, endemic to the arid SW region of Madagascar, was inferred to originate from an ancestor coming from the arid region of SW Africa. The similarity of habitats between source and colonized areas suggests the prevalence of niche conservatism, a common phenomenon in allopatric speciation following the colonization of a newly isolated region. Our results underscore the affinities between continental Africa and Madagascars montane floras. The main radiations of Helichrysum in Madagascars mountains occurred within the last 2 My, coinciding with a transition towards a cool, arid climate and the expansion of open habitats, and were likely driven by a combination of allopatric and ecological speciation.