Leaf clamp for fast attachment of a thermocouple sensor to the leaf surface. A. side view, B. bottom view. The clamp consists of an elastic and thin PVC - strip (1) with an opening (2) that is surrounded by a weak, glued - on miniature ring magnet (3). Inside the opening a thermocouple sensor is placed. Two small holes in the strip (5) act as a strain relief for the thermocouple wire (6). With a second ring magnet (8) the sensor can easily be fixed to the bottom side of the leaf (7). The inner diameter of the magnets (6 mm) ensures unimpeded solar irradiation (9) and leaf transpiration (10). The leaf clamp is particularly suitable for use in wet or humid environments as heat exposure chambers and microclimate stations.