A region of vegetation that develops in stagnant or slow-flowing water, such as that around a lake margin. Initially there is a layer of peat supporting numerous reeds. When this builds up above the water level many other species become established, including sedges and yellow flag iris. Swamps may also develop on water-retentive clays in desert and semidesert areas. Mangrove swamps are found along many tropical coasts. Mangroves are *halophytes
and grow in a tangled mass to a moderate height. The stems and the exposed roots are covered with red algae and various lichens. Stilt roots anchor them in the soft mud and help to retain silt, thus gradually enabling other species to grow.