Evolution of Heterostyly in Fagopyrum esculentum and F. cymosum Completed after Divergence of These Species

Morphometric analysis of short-styled (thrum) and long-styled (pin) flowers of Fagopyrum esculentum, F. cymosum, and interspecific F1 and F2 hybrids (F. esculentum × F. cymosum) demonstrated that the present time forms of heterostyly in F. esculentum and F. cymosum evolved independently, i.e., after the divergence of these species. It is known that heterostyly is controlled by the “switch” supergene GPA in combination with a polygenic background that provides “fine-tuning” of both thrum and pin flower phenotypes. The heterostyly supergene of F. esculentum and F. cymosum most likely originated in their common ancestor, with at least the pistil length determinant (subgene G) utilizing the same S-ELF3 gene in both cases (sequences of other subgenes have not yet been identified). However, the phenotypes of interspecific hybrids indicate clear differences in the polygenic systems that ensure species-typical heterostyly development. Thus, the model of heterostyly evolution in the genus Fagopyrum appears to be at least two-staged: (1) formation of the GPA supergene incorporating S-ELF3 as the pistil length determinant, and (2) independent fine-tuning of heterostyly morphology within diverged evolutionary lineages that became distinct species.