Plants’ vast variation in floral traits at a macroevolutionary level is often interpreted as the result of adaptation to pollinators. However, field studies often find no evidence of pollinator-mediated selection on flowers. This could be explained by periods of stasis, when selection is relaxed under stable conditions, followed by pollinator changes that provide innovative selection. We asked if periods of stasis are caused by stabilizing or absence of other forms of selection on floral traits, or by low trait heritability even if selection is present. We studied Ulex parviflorus , a plant predominantly pollinated by one bee species across its range. We measured heritability and evolvability of floral traits, using genome-wide molecular relatedness in a wild population, and combined this with estimates of selection. We found evidence for both stabilizing selection and low trait heritability as explanations for stasis in flowers. The area of the standard petal is under stabilizing selection, but the variability observed in the wild is not heritable. A separate trait, floral size, in turn presents high heritability, but is not currently under selection. We show how a stable pollination environment can lead to a lack of evolutionary change, yet maintain heritable variation to respond to future selection pressures.

A stable pollination environment limits current but not potential evolution of floral traits