Despite the great diversity in leaf structural and physiological traits, leaf structural traits appear to be coordinated with physiological function. It was observed that the petiole xylem structure is an important predictor of leaf gas exchange capacity, yet only a few studies have dealt directly with the question of how petiole xylem structure relates to leaf gas exchange. An understanding of the amount of variation that exists within a single species is also limited. In this study, we investigated the intraspecies coordination of leaf gas exchange and petiole xylem traits in two-year old seedlings of Ulmus leavis Pall. during optimal and drought conditions. It was found that all studied petiole xylem traits of the elm seedlings were positively correlated with each other. This shows that the development of petiole xylem structure is internally well-coordinated. Nevertheless, the lower correlation coefficients between some petiole xylem traits indicate that the coordination is also individually driven. Drought stress reduced all studied leaf gas exchange traits and significantly increased intraspecies variation. Drought stress also shifted the relationships between physiological traits. Moreover, there were more structure-function relationships under stress conditions. This indicates the importance of petiole xylem structure in dictating the water loss during drought stress. It could partly explain the inconsistencies between leaf structure-function relationships studied under optimal conditions. Although several structural-functional traits were related, the range correlation coefficients indicate that the internal coordination between structural-functional traits differs substantially between individual elm seedlings. These findings are very important in the context of expected climatic change, as some degree of phenotypic plasticity in structure-function relationships could ensure the survival of some individuals under different environmental conditions.