Floral morph variation mediated by pollinator functional groups under negative frequency-dependent selection in Limonium chrysocomum

Due to limited mating types and pollinator constraints, inter-morph mating and negative frequency-dependent selection in heterostylous plants may be weakened, reducing floral morphological and physiological stability and causing multidirectional floral morph variation. Although theory predicts such variation, its short-term evolutionary dynamics in natural populations are difficult to capture, with scarce empirical records and unclear long-term dynamics. Here, we investigated interannual floral morph variation, the heterostylous syndrome, and the pollination system in Limonium chrysocomum population, aiming to elucidate the variation and evolution pattern of morphs and driving factors. Our results showed that although reciprocal herkogamy was lacking or lost among morphs, strict heteromorphic incompatibility system and dimorphic pollen and stigma morphology were maintained, with no significant interannual differences in floral traits. The population comprised short-morph (S-morph), homostyly (H-morph), and long-morph (L-morph), two morphs may towards the H-morph.Under negative frequency-dependent selection, the mating-type frequencies shifted from initial unequal ratio to a balanced state. The homostyly evolved to promote legitimate pollen transfer rather than to facilitate self-pollination. Further analyses indicated that severe pollination limitation occurred in the early years, recently asymmetric pollen flow caused by variation of long- and short-tongued pollinators was associated with the shift from distyly to homostyly. However, the spatial arrangement of stigmas and anthers within flowers can affect the frequency of contact by long- and short-tongued pollinators. Therefore in heterostylous plants, pollinator effectiveness should be assessed not only by proboscis length but also combined with floral morphology and the spatial arrangement of sexual organs.