The morphology and development of tropical coastal wetlands
Mangroves can be defined as trees, shrubs, or palms, exceeding 0.5m in height that occur in the upper intertidal zone. They are not a single taxonomic group but rather a diverse range of plants with adaptations enabling survival in this otherwise inhospitable saline and anaerobic environment. Adaptations include viviparous propagules, for example, in many genera seeds remain attached and germinate on the tree and then are buoyant during a short aquatic dispersal phase. Many mangroves have developed mechanisms to tolerate salt, and the majority have root systems that enable the plants to respire despite being anchored in saturated, non-porous soils depleted of oxygen. Above-ground root systems include pneumatophores, prop roots, and buttresses, some of which provide structural support and most of which are covered with lenticels that promote gas exchange.