An aerial root may be defined as a root which, for part of the day at least, is exposed to the air. The mangrove mud is rather anaerobic (oxygen poor) and unstable and different plants have root adaptations to cope with these conditions.
Pneumatophores are erect roots that are some form of upward appendage or extension of the underground root system. Because these roots are exposed at least part of the day and not submerged underwater, the root system can obtain oxygen in an otherwise anaerobic substrate.
Prop and Stilt Roots
In Bakau (Rhizophora species), branched, looping roots arise from the trunk and lower branches. At this stage, they are known as prop roots.
In Bruguiera and Ceriops the horizontal roots growing just below the soil surface periodically grow vertically upwards then immediately loop downwards to resemble a bent knee. By repetition, a single horizontal root develops a series of knees at regular intervals.
From "A Guide to Mangroves of Singapore", Peter K. L. Ng and N. Sivasothi (editors)
Volume 1: The Ecosystem and Plant Diversity and Volume 2: Animal Diversity
Authors: Kelvin K. P. Lim, Dennis H. Murphy, T. Morgany, N. Sivasothi, Peter K. L. Ng,
B. C. Soong, Hugh T. W. Tan, K. S. Tan & T. K. Tan
BP Guide to Nature Series published by the Singapore Science Centre, sponsored by British Petroleum
© 2001 Raffles Museum of Biodiversity Research, The National University of Singapore & The Singapore Science Centre