Distyly is a well-known floral syndrome, first identified by Charles Darwin, characterised by the flowers within a population showing reciprocal placement of the anthers and stigma. In a recent study published in AoB plants, Jiang et al. use distyly as a model to determine how a key floral syndrome is shaped by nature. Primula chungensis, a distylous species with simultaneous homo-, short- and long-styled morphs, exhibits some variations in the length of style.
Using this species, Jiang et al. found that the stigma captured more compatible pollen as the separation between the stigma of the pollen receiver and the anther of the pollen donor decreased. Their results provide clear evidence for the disassortative pollination hypothesis proposed by Charles Darwin, which will be helpful for future understanding of the evolution of distyly. An alternative hypothesis for the evolution of distyly (e.g. selfing avoidance) might also be true, but is less likely, because self-incompatibility would greatly avoid self-fertilization for many distylous species.
Jiang, X.-F., Zhu, X.-F., & Li, Q.-J. (2018). Variation in the degree of reciprocal herkogamy affects the degree of legitimate pollination in a distylous species. AoB PLANTS, 10(3). https://doi.org/10.1093/aobpla/ply022