Accurate predictions of species distribution under current and future climate conditions require modeling efforts based on clear mechanistic relationships between climate variables and plant physiological functions. Vulnerability of leaves to xylem embolism is a key mechanistic trait that might be included in these modeling efforts. Here, we propose a simple set‐up to measure leaf vulnerability to embolism on the basis of the optical method using a smartphone, a light source, and a notebook. Our data show that this proposed set‐up can adequately quantify the vulnerability to xylem embolism of leaf major veins in Populus nigra and Ostrya carpinifolia, producing values consistent with those obtained in temperate tree species with other methods, allowing virtually any laboratory to quantify species‐specific drought tolerance on the basis of a sound mechanistic trait.
