The genus Begonia is one of the six largest angiosperm genera in terms of species number. Studies of such large genera, from the phylogenetic to the population level, can give insight into the processes that generate plant biodiversity. Several properties of Begonia suggest that restricted capability for gene flow through pollen and seed dispersal has been important in generating its species diversity. These are: (i) Monophyletic groups in Begonia show strongly restricted geographical distributions, suggesting repeated allopatric speciation events. (ii) The level of narrow range endemism of Begonia is very high, suggesting species ranges are dispersal limited. (iii) Widespread species are rare, and tend to show marked morphological variation, suggesting low intra-specific gene flow over moderate to large scales. (iv) Begonia has over 1400 species, but few obvious major innovations - the majority of Begonia appear broadly ecologically similar. Species from the Socotra archipelago (B. socotrana and Begonia sp. nov.) and South Africa (B. sutherlandii) are being used to investigate gene flow and population structure in Begonia, with the aid of microsatellite markers. A combination of population genetic, phylogenetic and distributional data represents a potential data set for understanding the processes that have led to these observed patterns of biodiversity.

Key words: Begonia, microsatellites, speciation