Mangrove Tree

The family Rhizophoraceae contains about 100 species of woody plants, all of which are tropical or subtropical in distribution. The most important of the tree-sized species are in the genera Avicennia, Bruguiera, Ceriops, and Rhizophora.

The red mangrove (Rhizophora mangle) is abundant in mangrove forests of south Florida, the Caribbean, and Central and South America. This species has distinctive, round, stilt-roots, which emerge from aerial parts of the stem and then curve downwards to grow into the sediment. The red mangrove also retains its ripe seeds on its branches, where they germinate aerially, extending a radicle up to 10 in (25 cm) long. This sort of germination system is known as vivipary, and is analogous in some respects to the bearing of live young by animals. The germinated seedlings eventually detach from the parent tree, and may plop upright into the mud and establish a new plant, or they may float for a while until they become lodged in sediment after a longer-range dispersal from the parent. The established seedlings of red mangrove send out prop-roots, which quickly become firmly anchored and help to accrete mud around the plant. Young plants of this sort are abundant along the leading edge of developing stands of red mangrove, with older, larger trees occurring further into the stand. The individual stands often occur as discrete mangrove "islands," which may eventually coalesce as an extensive forest.

The black mangrove (Avicennia nitida) is also abundant in mangrove forests of Florida, the Caribbean, and Latin America. This species has radially spreading, underground roots from which emerge numerous, vertically growing pneumatophores, or extensions of the roots that emerge from the mud. The pneumatophores are exposed to the atmosphere during low tide, and are useful in conducting oxygen to the underwater tissues of the plant, which grow in an anaerobic environment. Black mangroves often do not reproduce well beneath their own closed canopy, and when their stands senesce and die back, the site may convert into a relatively open community dominated by plants of salt marshes and protected mudflats.