Trees growing in flooded soils require special adaptations if they are to survive this watery habitat. One of the problems they face is how to make sure their roots receive sufficient oxygen to function properly.
In much the same way that we can use snorkels to breathe if we want to keep our heads underwater, trees with submerged roots develop specialised root structures known as pneumatophores.
Brave the waters of a mangrove swamp and you will see these slender, stick-like structures in their thousands, protruding from the soil and shallow water.
Pneumatophores are usually about 30cm in length. They take in oxygen through minuscule pores known as lenticels and transport it down into the deeper root system, creating a thin, oxygen-rich layer around the very base of the plant.
Indeed, experiments have revealed that if the pneumatophores are covered, the transportation of oxygen ceases and the mangroves die.
Another adaptation of mangrove trees are stilt roots, or prop roots – pitchfork-like extensions from the trunk that grow downwards into the sediment, helping to stabilise the plants against tides and flooding.
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Main image: Trees with submerged roots develop snorkel-like structures known as pneumatophores. © Auscape/Getty