Have you ever heard about Pneumatophores? Almost all of us think that roots always found underground.
Well, roots are not always found below the soil. Though, most of the roots are 'Positively Geotropic' – which means that they grow downwards towards the gravity, yet there are many exceptions to this. Some roots are negatively geotropic. Roots are sometimes aerial in nature. The classic example of this are the Pneumatophores – the breathing roots.
Pneumatophores are specialized ‘breathing’ roots that develop in some plant species growing in waterlogged or strongly compacted soils, e.g. mangroves.
The aerial part of the root contains many pores, enabling gas exchange with the atmosphere. Internally, a well developed system of intercellular spaces allows gases to diffuse throughout the submerged portion of the roots. Because these roots are exposed and not submerged underwater, the root system performs the function of obtaining oxygen which is otherwise difficult to obtain from the water-looged soil.
In some species these roots are pencil-like and grow up to only 30 cm tall, whereas in others, they grow more slowly to become woody and may even reach 3 m in height, though most will be less than 50 cm tall. The widely spreading horizontal roots, from which the pneumatophores grow, improve anchorage in the unstable mud.