Phenotypic plasticity and plant adaptation*

This paper focuses on phenotypic plasticity as a major mode of adaptation in plants. A methodological critique examines difficulties in studying plasticity, including the conceptually critical distinction between functionally adaptive and inevitable aspects of response. It is argued that plasticity studies depend critically upon the genotypic sample, the choice of environmental factors and factor states, and the definition of phenotypic traits. Examples are drawn from recent studies showing adaptive response by genotypes to physical aspects of the environment, as well as to biotic factors such as neighbour density and the presence of bacterial symbionts. Alterations of offspring traits by parental plants of Polygonum persicaria are discussed as a cross-generational aspect of plastic response to environment. Finally, individual plasticity and local ecotypes are examined as alternative bases of species ecological breadth, and methodological problems in distinguishing these alternatives are discussed.