The emergence of new techniques in plant science, including molecular and phenomic tools, presents a novel opportunity to re-evaluate the way we examine the phenotype. Our increasing capacity for phenotyping means that not only can we consider increasing numbers of species or varieties, but also that we can effectively quantify the phenotypes of these different genotypes under a range of environmental conditions. The phenotypic plasticity of a given genotype, or the range of phenotypes, that can be expressed dependent upon environment becomes something we can feasibly assess. Of particular importance is phenotypic variation that increases fitness or survival – adaptive phenotypic plasticity. Here, we examine the case of adaptive phenotypic plasticity in plant water use traits and consider how taking an ecological and evolutionary perspective on plasticity in these traits might have relevance for agriculture, horticulture and the management of native and invasive plant species in an era of rapid climate change.