Frequent colonization and little in situ speciation in Senecio in the tropical alpine-like islands of eastern Africa

Abstract

Floras of continental habitat islands, like those of islands, originate mostly through colonization, which can be followed by in situ speciation. We here address the question of the relative importance of colonization and in situ diversification in the high-altitude areas of the eastern African high mountains, the tropical Afroalpine Region, using the most species-rich genus in the region, Senecio, as an example. METHODS: We expanded earlier Senecioneae phylogenies by adding more tropical African species and analyzed our phylogenetic tree biogeographically. KEY RESULTS: Senecio contains at least fi ve clades with tropical African species, all of them containing tropical afroalpine species. Between four to 14 independent colonization events into the tropical Afroalpine most likely from montane regions in southern Africa were found. Additionally, relationships of tropical afroalpine species to Palearctic and South American taxa were identifi ed. Although some in situ diversifi cation occurred in Senecio in the tropical Afroalpine, the resulting number of species per clade is never higher than seven. C ONCLUSION: Like other genera, S enecio colonized the tropical Afroalpine several times independently. Comparison with Mt. Kinabalu, a small tropical alpine-like region in Southeast Asia, and alpine-like regions in the Andes implies that rates of in situ speciation might be linked to area size.