Plants are not collections of independent traits. Rather, they are integrated wholes whose components are interlinked biochemically, functionally, and developmentally. A trait's response (or lack thereof) to an environmental stimulus influences, or even constrains, concurrent responses in other traits, through common control pathways, compensatory plasticity, or other mechanisms of phenotypic integration. This symposium explores the tension between single-trait reaction-norm evolution, and whole-plant trait integration. The papers describe a range of integrating processes and discuss consequences for the evolution of integrated responses to the environment.

Key words: constraint, evolution, phenotypic integration, plasticity, reaction norm