When a cuvette is not a canopy: A caution about measuring leaf temperature during gas exchange measurements

•Leaf temperatures measured across a range of air temperatures suggest homeothermy.•Measurements made with no leaves in the cuvette also exhibit homeothermy.•The design of a popular gas exchange system drives this behavior.•Modeled leaf temperatures based on energy balance are more representative.•Extrapolation of leaf thermoregulation to natural settings is unrealistic.