mangrove, any of certain shrubs and trees that belong primarily to the families Rhizophoraceae,Acanthaceae, Lythraceae, Combretaceae, andArecaceae; that grow in dense thickets or forests along tidal estuaries, insalt marshes, and on muddy coasts; and that characteristically have prop roots—i.e., exposed supporting roots. The termmangrove also applies to thickets and forests of such plants. Respiratory or knee roots (pneumatophores) are characteristic of many species; they project above the mud and have small openings (lenticels) through which air enters, passing through the soft spongy tissue to the roots beneath the mud.

Mangroves are extremely important to the coastal ecosystems they inhabit. Physically, they serve as a buffer between marine and terrestrialcommunities and protect shorelines from damagingwinds,waves, andfloods. Mangrove thickets improve water quality by filteringpollutants and trapping sediments from the land, and they reduce coastalerosion. Ecologically, they providehabitat for adiverse array of terrestrial organisms, and many species of coastal and offshorefish andshellfish rely exclusively on mangroves as their breeding, spawning, and hatching grounds. Because of their high salt tolerance, mangroves are often among the first species to colonize mud and sandbanks flooded byseawater, but an increase in coastal development and altered land use led to a decline in global populations. Several species are listed asvulnerable orendangered on theInternational Union for Conservation of Nature (IUCN)Red List of Threatened Species.

Mangrove flora along the Atlantic coast of tropicalAmerica and along the coast of theGulf of Mexico toFlorida consists chiefly of thecommon, or red, mangrove (Rhizophora mangle) of the family Rhizophoraceae and theblack mangroves (usuallyAvicennia nitida, sometimesA. marina) of the family Acanthaceae. Mangrove formations inSoutheast Asia also includeSonneratia of the family Lythraceae and the nipa palm (Nypa fruticans) of the family Arecaceae. The trunks and branches of most mangrove species constantly produce adventitious roots, which, descending in arched fashion, strike at some distance from the parent stem and send up new trunks.

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Plants: From Cute to Carnivorous

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The common mangrove grows to about 9 metres (30 feet) tall. Theleaves are 5 to 15 cm (2 to 6 inches) long, opposite, oval or elliptic, and smooth-edged; they are thick, have leathery surfaces, and are borne on short stems. Theflowers are pale yellow. While thefruit is still attached to the parent branch, the long embryonicroot emerges from theseed and grows rapidly downward. When this propagule falls, the young root is in the correct position to be driven into the mud; theplant being thus rooted, the shoot makes its appearance. The young root may grow to such a length that it becomes fixed in the mud before the fruit separates from the parent tree.

The black mangrove, usually ofmoderate height, sometimes grows 18 to 21 metres (59 to 69 feet) tall. The leaves are 5 to 7.5 cm (2 to 3 inches) long, opposite, oblong or spear-shaped; the upper surface is green and glossy, the lower surface whitish or grayish. The white flowers are small, inconspicuous, and fragrant and are frequented by honeybees for their abundant nectar.

Thewood of some species is hard and durable. The astringentbark yields a water-soluble tanning substance. The fruit of the common mangrove is sweet and wholesome.