Assessing floral trait variation in Platanthera dilatata (Orchidaceae) across an elevational gradient.

Flower morphology often changes over altitude, although the patterns themselves can be variable, with flowers being either smaller or larger. Floral trait variation is often considered in the context of pollinator-mediated selection. However, other explanations, including underlying genetics and plasticity, resource availability and floral enemies have been proposed. Here, we assess 10 floral traits in Platanthera dilatata var. dilatata across an elevational gradient on Vancouver Island, British Columbia, Canada, to determine if floral traits vary with altitude. We find that floral traits are larger at the lowest elevation site. However, much of the floral trait variation appears to be driven by temperature, which is not necessarily correlated with the altitudinal gradient. Given the intrinsic link between climate and resource availability, we suggest that resource availability confers a local selection pressure on floral trait size that may be balanced at larger spatial scales by antagonistic pressure from shared pollinators. Direct investigations of the environmental and genetic factors driving floral trait variation are recommended.

Supplementary information: The online version contains supplementary material available at 10.1007/s44372-024-00071-6.