About 110 species are characteristic plants of mangrove vegetation, out of more than 250,000 species of vascular plants, indicating that this is a tough environment for plants. At a given mangal location, it would be highly unusual to collect three dozen species, and some sites, especially marginal subtropical locations and recently established plots, may have only one or two species. The mangrove species of the world are all perennials, and none can grow either where any freezing occurs or where the water temperature is seasonally cold. Hence, temperature factors limit the poleward extent of this type of forest. [Avicennia can tolerate up to twelve hours of freezing air temperatures.]
Mangrove species have evolved from nonmangrove plant lineages independently many different times, and therefore occur in more than 30 families of dicotyledons, as well as the monocotyledons Nypa (a palm, family Arecaceae), Crinum angustifolium (family Amaryllidaceae; plant and flowers), and Pandanus (screwpines, family Pandanaceae) and ferns of the genus Acrostichum.
The mangrove family, Rhizophoraceae, is virtually always present at mangal sites. The genus Rhizophora is exceedingly common around the world, although none of the individual species is truly cosmopolitan. Red mangrove, R. mangle, is, of these, the most widespread species, occurring along the Pacific coast of the Americas from 28 degrees north latitude in Baja California and Sonora to northwestern South America and the Galapagos Archipelago, on the eastern side of the Americas from southernmost Florida to southern Brazil, and along tropical West Africa. In the Old World, Bruguiera gymnorrhiza is especially widespread, ranging from East Africa to eastern Australia, Samoa in the Pacific Basin, and the Ryukyu Islands in Asia. There are other exceedingly widespread species of this family in Old World mangal, including the two species of Ceriops and Kandelia candel.
Avicennia spp., black mangrove, is ubiquitous in mangal. In the Western Hemisphere, A. germinans is codominant with red mangrove, R. mangle, and a variant of this Avicennia occurs along the coastline of West Africa. Two other species in the genus may be found in the New World. Avicennia marina is the most widespread species of the Old World, extending from East Africa to Fiji in Polynesia and the North Island of New Zealand, and occurring at the coldest localities in New Zealand, subtropical China (26 degrees north latitude), and southeastern Australia (Victoria, at 38.45 degrees south latitude).
Sonneratia alba (family Sonneratiaceae) is characteristic of the tropical mangal of the Old World, generally appearing with Avicennia, the Rhizophoraceae, Excoecaria agallocha (family Euphorbiaceae), Xylocarpus granatum (family Meliaceae), Aegiceras corniculatum (family Myrsinaceae; a shrubby understory), Osbornia octodonta (family Myrtaceae), and Lumnitzera racemosa (family Combretaceae).
In mangal of the Americas, diversity of the woody species is much lower. In addition to Rhizophora mangle and Avicennia germinans, a visitor to a New World mangrove swamp is likely to find Laguncularia racemosa (family Combretaceae) and either Conocarpus erectus (family Combretaceae) or Pelliciera rhizophorae (family Pellicieraceae).
The nipa palm, Nypa fruticans, is a very aggressive colonizer of estuarine banks and lagoons of the Old World tropics. This plant crowds out all potential competitors by forming subterranean rhizomes in the mud, from which arise the pinnately compound leaves. The other monocotyledon of mangal, species of Pandanus, most commonly grows in coastal swamps than within the dense thicket of mangal. The only terrestrial ferns of mangal are species of Acrostichum, which tend to grow in less saline microhabitats and also can tolerate shade, but are still very tolerant of salinity.