Sexual organ reciprocity in distylous primroses

The main morphological characteristic of heterostyly is the reciprocal placement of anthers and stigmas in two distinct floral morphs; however, the partitioning of reciprocity within and between closely related species remains unknown. Keller et al. examine six floral traits in both floral morphs of 15 allopatric populations of Primula elatior, P. veris and P. vulgaris, and estimate anther–stigma reciprocity. They find that differences in anther and stigma heights between the species are of the same magnitude or larger than intraspecific differences that alter pollen flow within other heterostylous systems. Therefore, it is possible to suggest that considerable reductions of sexual organ reciprocity between species may lower interspecific pollen flow, with potential effects on reproductive isolation.