Cuticular transpiration is the loss of water vapour directly through the plant cuticle rather than through the stomata. Although the cuticle is designed to be water-resistant, it is not completely impermeable, and a small amount of water can diffuse through it and escape into the atmosphere.
In most healthy leaves, cuticular transpiration accounts for only a small fraction of total water loss because stomatal transpiration is the dominant pathway. However, its importance increases when stomata are closed, such as during drought, darkness, or environmental stress. Species with thicker cuticles and heavier wax deposits generally have lower rates of cuticular transpiration.
Environmental conditions such as high temperature, low relative humidity, strong airflow, and cuticle damage can increase cuticular water loss. Solvents, abrasives, and some pesticides may disrupt cuticular waxes, increasing cuticle permeability and accelerating water loss even when stomata remain closed.
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