POPULATION STRUCTURE,BIOMASS ALLOCATION,AND PHENOTYPIC PLASTICITY IN MURDANNIA KEISAK (COMMELINACEAE)

Field and glasshouse studies were used to explain differences in plant biomass, shoot length, and reproductive effort in four populations of a wetland annual herb, Murdannia keisak. Populations were chosen from continually thermally disturbed, intermittently thermally disturbed, revegetating, and undisturbed portions of a floodplain forest in South Carolina, USA. Plants in the two thermally disturbed areas were shorter, flowered earlier in the autumn, and produced more and smaller seeds than plants in revegetating and undisturbed sites. Reproductive effort was higher in populations from undisturbed and revegetating sites than in the two thermally disturbed sites. Generally, differences observed in the field were not expressed in the glasshouse plants. Glasshouse experiments suggested that most of the observed among-population differences in size and reproductive effort in the field study were a result of a plastic response to water depth and light. The combination of field and glasshouse data showed that this wetland weed adjusts readily to newly disturbed habitats, thus spreading rapidly and maintaining local dominance.