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Clonal replicates of Spartina anglica C. E. Hubbard were reciprocally transplanted into cleared plots and undisturbed vegetation in three adjacent zones on the Dee Estuary salt marsh, Cheshire, England. The aim of the investigation was to examine whether clones from these populations show a differential response to the range of naturally occurring environmental variation. Clone survival was significantly lower in the pioneer zone relative to the sward and mature marsh zones and was greatest in plants from the pioneer population in all transplant sites. Tiller number per plant was consistently greater in the pioneer population, increased with increasing marsh elevation and the removal of natural vegetation in the mature zone, and, for the pioneer and mature populations, showed a significant clone × environment interaction effect. The norms of reaction showed marked differences between clones in the pattern of response to environmental variation, but joint regression of clone means on overall means showed that very few clones had a linear response. Several morphological characters showed significant interactions with environmental effects in ANOVA, but only for total plant biomass in the pioneer population did this reflect a linear increase in more favourable environments. Differences in overall stature quantified by the pattern of morphological character correlations indicated the occurrence of different morphological forms within the populations. The differences in performance and plasticity are discussed in the context of the successional development of these populations, and the possible influence of age-related somatic variation. [ABSTRACT FROM AUTHOR]