text: Alarm photosynthesis is a variation of photosynthesis where calcium oxalate crystals function as dynamic carbon pools, supplying carbon dioxide (CO) to photosynthetic cells when stomata are partially or totally closed. This biochemical appendance of the photosynthetic machinery is a means to alleviate the perpetual plant dilemma of using atmospheric CO for photosynthesis and losing water vapor, or saving water and reducing photosynthesis. The function of alarm photosynthesis seems to be rather auxiliary to the overall photosynthetic performance. It supports a low photosynthetic rate, aiming at the maintenance and photoprotection of the photosynthetic apparatus rather than a substantial carbon gain.