Colobanthus quitensis (Kunth, 1831) Bartling (Caryophyllaceae) is characterized by a wide latitudinal distribution, ranging between the tropical high Andes and the Antarctic Peninsula. Although both habitat types are characterized by cold and freezing temperatures, important microclimatic differences exist during the growing season. Hence, important differences in the response of the photosynthetic apparatus to abiotic factors could be expected between Antarctic and Andean populations of C. quitensis. We studied the relationship between net photosynthesis, leaf temperature and light intensity in two populations of C. quitensis, one from La Parva in the Andes of central Chile and the other from King George Island, in the Maritime Antarctic. Plants from both populations were grown in the laboratory at 15 °C under 250 μmol photons m-2 s-1, with a 16/8 h light/dark photoperiod. Twenty plants (about two months old) of each population were transferred to a 4 °C chamber with the same light and photoperiod conditions as above to assess the photosynthetic acclimation capacity. At 15 °C, populations differed in their optimum leaf temperature for photosynthesis, being 24.0 °C in individuals from the Andes and 18.6 °C in individuals from the Antarctic. In contrast, Antarctic individuals showed the highest net photosynthesis rate under both temperature treatments, with the lowest light compensation and saturation points. Antarctic individuals had higher photosynthetic activity at lower temperatures compared to individuals from the Andes. Our results suggest that C. quitensis has adapted photosynthetic performance of individuals growing in different localities to the prevailing climatic conditions. Differences in photosynthetic responses to temperature and light are discussed in relation to ecotypic differentiation between two populations studied