One postulated prerequisite for phenotypic plasticity to evolve in a population is gene flow among its members. To test this hypothesis, I compared the phenotypic plasticity of 3 congeneric nut-sedges (Cyperus: Cyperaceae) that are similar in size, cohabit sandy beaches, yet differ in their reproductive strategies. Cyperus strigosus reproduces sexually by seed, C. dentatus asexually by bulbils, tubers, and rhizomes, and C. esculentus by a combination of sexual seed and asexual rhizomes and tubers. I predicted that C. strigosus and C. esculentus would be most plastic due to their potential for gene migration, while the asexual C. dentatus would be less plastic. Progeny arrays from nine genotypes of each species were grown in a series of eight environments in growth chambers. I measured 15 vegetative and reproductive traits at maturity. Analysis of covariance indicated a plastic response to the environment for all traits as well as genetic variation in phenotypic plasticity for all but vegetative allocation traits. Indices of plasticity for each genotype were highest for C. esculentus genotypes for vegetative traits and for C. strigosus genotypes for reproductive traits. These results support the hypothesis that non-zero gene migration enables the evolution of phenotypic plasticity.