Rhizophora mangle, known as the red mangrove, is distributed in estuarine ecosystems throughout the tropics. Its viviparous "seeds," in actuality called propagules, become fully mature plants before dropping off the parent tree. These are dispersed by water until eventually embedding in the shallows.
Rhizophora mangle grows on aerial prop roots, which arch above the water level, giving stands of this tree the characteristic "mangrove" appearance. It is a valuable plant in Florida, Louisiana, and Texas costal ecosystems. In its native habitat it is threatened by invasive species such as the Brazilian pepper tree, (Schinus terebinthifolius). The red mangrove itself is considered an invasive species in some locations, such as Hawaii, where it forms dense, monospecific thickets. R. mangle thickets, however, are known to provide nesting and hunting habitat for a diverse array of organisms, including fish, birds, and crocodiles.
Red mangroves are found in subtropical and tropical areas in both hemispheres, extending to approximately 28°N to S latitude. They thrive on coastlines in brackish water and in swampy salt marshes. Because they are well adapted to salt water, they thrive where many other plants fail and create their own ecosystems, the mangals. Red mangroves are often found near white mangroves (Laguncularia racemosa), black mangroves (Avicennia germinans), and buttonwood (Conocarpus erectus). Through stabilisation of their surroundings, mangroves create a community for other plants and animals (such as the mangrove crab) to survive. Though rooted in soil, mangrove roots are often submerged in water for several hours or on a permanent basis. The roots are usually sunk in a sand or clay base, which allows for some protection from the waves.
Red mangroves are easily distinguishable through their unique prop roots system and viviparous seeds. The prop roots of a red mangrove suspend it over the water, thereby giving it extra support and protection. They also help the tree to combat hypoxia by allowing it a direct intake of oxygen through its root structure.
A mangrove can reach up to 80 feet (24 m) in height in ideal conditions; however, it is commonly found at a more modest 20 feet (6.1 m). Its bark is thick and a grey-brown color. Mangrove leaves are 1–2 inches (2.5–5.1 cm) wide and 3–5 inches (7.6–13 cm) broad, with smooth margins and an ellipse shape. They are a darker shade of green on the tops than on the bottoms. The tree produces pale yellow flowers in the spring.
As a viviparous plant, R. mangle creates a propagule that is in reality a living tree. Though resembling an elongated seed pod, the fully-grown propagule on the mangrove is capable of rooting and producing a new tree. The trees are hermaphrodites, capable of self pollination or wind pollination. The tree undergoes no dormant stage as a seed, but rather progresses to a live plant before leaving its parent tree. A mangrove propagule may float in brackish water for over a year before rooting.
Propagules growing before dropping from the parent plant. (BioBay, Vieques)