Mertensia fusiformis (Boraginaceae) is a spring-flowering perennial showing pronounced intraspecific variation in style length and stigma–anther separation. Forrest et al. show that population-level variation in flowering time, driven by patchiness in timing of snowmelt, causes different populations to experience different temperature regimes during flowering and functionally distinct suites of pollinators. The interaction between plant and pollinator phenology in particular appears to be involved in maintaining style-length variation in this species.
