The pollinator-driven ecological speciation model has frequently been invoked to explain plant richness in biodiversity hotspots. Here, we test the hypothesis that high species diversity in southern Africa, one of the world's most floristically rich regions, has primarily been driven by ecological shifts in pollination systems, by focusing on Gladiolus (260 species), a flagship example of a clade with diverse pollination biology. We use phylogenetic methods to estimate rates of transitions between the seven highly specialized pollination strategies in Gladiolus. We find that pollination systems have evolved multiple times and that some pollination strategies arose by a variety of evolutionary pathways. Pollination shifts account for up to a third of all lineage splitting events in the genus, providing partial support for the pollinator-driven speciation model. Transitions from the ancestral pollination mode to derived systems have also resulted in increased rates of diversification, suggesting that certain pollination systems may speed up speciation processes, independently of pollination shifts per se. This study confirms that frequent pollination shifts have played a role in driving high phenotypic and species diversity, but suggests that additional factors need to be invoked in order to account for the spectacular diversification in southern African Gladiolus.