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Premise of research: Local adaptation ultimately arises as a result of adaptive divergence in phenotypic characters. Within a species, a large portion of the phenotypic traits that confer local adaptation must be physiological characters. Yet few studies consider adaptive divergence in physiological characters or estimate genetic variation within populations for physiological traits that may confer local adaptation. Here I test the hypothesis that there is genetic variation within and between populations of a C3-C4 intermediate for theCO2 compensation point (G) and other photosynthetic traits. In addition to local adaptation, population-level variation in photosynthetic characters of C3-C4 intermediates reflects the potential for evolution of more C4-like photosynthesis. Methodology: I chose two populations of Mollugo verticillata, one from a relatively cool climate and one from a warm climate. I quantified variation within and between populations by measuring photosynthetic physiology at 247 and 357C, temperatures that match the average maximums during the growing season at the populations' native sites. Pivotal results: I detected little evidence of genetic variation within populations for G and carboxylation efficiency, but there was temperature-dependent population variation for G, where the population from the cool climate had a lower average G at 247C. Apparent chlorophyll concentration was also greater in this population at both temperatures. Conclusions: The results demonstrate that there has been divergence among populations in G. Interestingly, the population from the cooler climate had lower G at 247C. There is little evidence of adaptive evolutionary potential within populations; estimates of broad-sense heritability were not significant even when pooling samples from both populations to increase the overall sample size. Adaptation of more C4-like photosynthesis may proceed through the evolution of other physiological characters not directly related to concentrating carbon. [ABSTRACT FROM AUTHOR]