Deschampsia antarctica and Colobanthus quitensis are extremophile species thriving from the Andes to the Subantarctic regions. Although they share this gradient with other species, notably, they are the only flowering plants growing naturally in Antarctica. These species exhibit traits typical of xeromorphy, such as high leaf mass area (LMA) and leaf density (LD), which influence mesophyll conductance and photosynthesis. However, under warmer conditions, Antarctic plants reduce their LMA and LD, optimizing photosynthesis and hydraulic conductivity, reflecting their ability to adjust these traits in response to temperature variations. While considerable research has focused on their physiological responses in Antarctica, it remains unclear whether these traits are exclusive to Antarctic provenances or are also found in populations outside Antarctica or in related species from similar environments. We hypothesize that the traits related to carbon assimilation and hydraulics in Antarctic species are specific adaptations to extreme Antarctic conditions and may not be present in Subantarctic provenances or in phylogenetically related species in other stressful environments. We grew D. antarctica and C. quitensis from Antarctic and Subantarctic provenances, along with related species: Deschampsia caespitosa, Avenella flexuosa, and Colobanthus apetalus, at 5 degrees C, 15 degrees C, and 23 degrees C. Both Antarctic and Subantarctic D. antarctica showed consistent coordination of photosynthesis and hydraulic traits across temperatures. C. quitensis showed provenance-specific responses, possibly due to ecotypic differentiation, with C. apetalus situated closely to Subantarctic C. quitensis in comparison with the Antarctic one. This research highlights some physiological responses of Antarctic plants and their adaptation to extreme climates.