Floral morphology modulates the functionality of distyly in sea lavenders (Limonium)

Distyly promotes cross-pollination via reciprocal herkogamy and heteromorphic self-incompatibility, and how its functionality is maintained in species with contrasting corolla morphologies is worth further study. Using eight Limonium species (four long-tubular, four short-tubular) across 25 populations from Xinjiang, China, we examined whether corolla morphology affects distylous syndrome, reproductive success and the relationship between reciprocity and pollen deposition. All species exhibited pollen-stigma dimorphism and high fruit set from inter-morph pollination but were almost sterile from selfing/intra-morph pollination. However, long-tubular and short-tubular flowers showed divergent functional strategies. Long-tubular species displayed smaller variation in herkogamy but suffered significant pollen limitation under open pollination, with fruit set markedly lower than hand cross-pollination. In contrast, short-tubular species showed greater floral morph variation, broader variation ranges in herkogamy and higher natural fruit set with no pollen limitation. Critically, in the long-tubular L. chrysocomum, lower reciprocity was associated with reduced illegitimate pollen deposition on papillate stigmas, challenging the assumption that higher precision always enhances function. These results revealed that corolla morphology modulates distyly functionality through two distinct pathways: in addition to pollen-stigma dimorphism, long-tubular flowers (L. chrysocomum) maintain distyly through optimized reciprocity; short-tubular flowers exhibit a greater reliance on dimorphism alone. Our findings highlight the role of floral architecture in shaping the ecological and evolutionary dynamics of distyly.