The pistil as a traffic light: Yellow‐to‐red color change likely influences pollinator visitation patterns in Saxifraga fortunei (Saxifragaceae)

Societal Impact Statement Flowers can communicate reproductive status to pollinators through visual cues. In Saxifraga fortunei , pistils often changed from yellow to red after pollination, and hoverflies and honeybees preferentially visited flowers with yellow pistils. This pattern suggests that a post‐pollination color shift confined to the pistil can reduce revisits to already pollinated flowers and concentrate visitation on flowers still capable of seed set, thereby improving pollination efficiency in dense floral displays. These findings broaden current views of floral signaling by demonstrating that a floral organ other than the perianth can function as a dynamic visual cue. Summary Floral color change during anthesis has been documented in many angiosperms and is widely regarded as a visual signal influencing pollinator visitation. Nevertheless, direct empirical evidence remains scarce, and no study has demonstrated that color change confined to floral organs other than petals or sepals is associated with pollinator visitation patterns. We investigated pistil color change in Saxifraga fortunei by assessing its association with pollinator activity in natural populations and laboratory hand‐pollination and wounding experiments. We also surveyed floral morphology in closely related taxa through field observations, literature review, and online image databases. In S. fortunei , pistils often changed from yellow to red after pollination, and reddened pistils consistently showed pollen tubes reaching the ovules, whereas yellow pistils often exhibited incomplete or absent pollen tube growth. Field observations showed that hoverflies and honeybees visited only flowers with yellow pistils, a pattern suggesting that pistil color change underlies reduced visitation following pollination and may enhance pollination efficiency. Comparative surveys revealed that similar pistil color change occurs in several related species, suggesting that they may share the same pollination strategy as S. fortunei . Overall, our study provides the first empirical evidence that color change restricted to the pistil is associated with changes in pollinator visitation and highlights previously overlooked roles of non‐perianth floral organs in plant–pollinator interactions. Further investigation is needed to clarify how this trait evolved and diversified among related taxa.