Genotypic Similarity of Large and Small Individuals in a Natural Population of the Annual Plant Stephanomeria Exigua Ssp. Coronaria (Compositae)

SUMMARY The distribution of individual size in populations of the annual plant Stephanomeria exigua Nutt. ssp. coronaria (Greene) resembles that of many plant species, being composed of a few large individuals and a very large number of small ones. Gross size differences might result in substantial fitness differentials if they reflect genotypic differences. Electrophoresis of enzymes and a uniform garden study were used to analyse the extent of genotypic similarity between large and small plants. No significant genotypic differences were observed, and their progenies had similar sizes and growth rates. The genetic similarity of individuals at opposite extremes of the size distribution suggests that differences in plant size and fecundity in highly plastic annual plants primarily reflect environmental factors and are unlikely to be the basis of evolutionary changes.