Mangroves have developed three systems to protect themselves from salt: exclusion, excretion and concentration. Excluders have special tissues in their roots and lower stems (areas inundated by the tide) which act as a barrier to salt and prevent it from entering the plant's tissues.
All species are excluders to some extent. Some species such as the Stilted Mangrove can exclude up to 90% of the salt. Traditional coastal cultures know that fresh water can be obtained from mangroves. Excreters, such as the Grey Mangrove, use special glands on their leaves to concentrate the salt and allow it to evaporate off the surface of the leaves. These glands are thousands of times more effective in concentrating and removing salt than our sweat glands.
You may see mangrove leaves covered in a film or crust of salt as a result of this system. The last method, concentration, is where salt is moved to old leaves, flowers, bark or fruits which then drop off, taking the concentrated salt with them.
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