Population variation in Spartina anglica C. E. Hubbard

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Abstract
Summary: Replicated clones from ten populations of Spartina anglica C. E. Hubbard were grown in a common garden experiment to determine whether the phenotypic variation previously observed in natural habitats was due to inherent differences between clones. For a range of morphological characters, mean differences between populations, and clonal repeatability, were very low. Different morphological forms were, however, evident from differences in character correlations. Thus, morphological variation appears to be dominated by phenotypic plasticity with a limited amount of possibly genetic differences distinguishing different morphological forms. No differences in the relative variability of morphological characters were recorded between populations sampled from successionally adjacent salt‐marsh zones, although the oldest population, from Poole Harbour, contained significantly less morphological variation than other populations. The pattern of (a) flowering during the first year of the experiment, (b) clone survival, and (c) clonal growth, showed that the vigour of clones sampled from four successionally mature populations was significantly less than that of the other populations. It is suggested that these consistent differences between populations are due to an age‐related decline in vigour of clonal material and, thus, due to somatic variation rather than to genetic differences between populations. The ecological implications of this interpretation are discussed in relation to the origin of S. anglica and the successional development and ‘die‐back’ of natural populations.