The spatial separation of stigmas and anthers (herkogamy) functions to reduce self-pollination and avoid interference between pollen dispersal and receipt. Little is known about the evolutionary relationships among the main forms of herkogamy. Kissling and Barrett examine those relationships in Exochaenium, a genus of African herbs, using phylogeny reconstruction. They find that distyly originated once from an ancestor with approach herkogamy, supporting a theoretical model proposed by Lloyd and Webb in 1992. The results demonstrate the lability of sex-organ deployment and implicate pollinators, or their absence, as playing an important role in driving transitions among herkogamic and non-herkogamic conditions.
