Common Name: White Mangrove

General Information

White mangrove is an evergreen shrub or small tree with an open branched, rounded crown; usually growing 1 - 10 metres tall but sometimes, especially in northern Australia, up to 25 metres tall[, ]. The bole, which can be straight or crooked, is 20 - 40cm in diameter[]. Growing in the tidal mudflats, it develops roots with many vertical breathing roots above soil level[]. The leaves excrete excess salt through pores, and salt crystals are commonly present on the leaves[].
A multipurpose tree, it is harvested from the wild for use as an insect repellent, dye plant, source of tannins, timber etc.
This species is widespread and common throughout its range. It is a fast growing and fast regenerating, hardy species. It is threatened by the loss of mangrove habitat throughout its range, primarily due to extraction and coastal development, and there has been an estimated 21% decline in mangrove area within this species range since 1980. Mangrove species are more at risk from coastal development and extraction at the extremes of their distribution, and are likely to be contracting in these areas more than in other areas. It is also likely that changes in climate due to global warming will further affect these parts of the range. Although there are overall range declines in many areas, they are not enough to reach any of the threatened category thresholds. The tree is classified as 'Least Concern' in the IUCN Red List of Threatened Species(2011)[].

Known Hazards

The young seed leaves may contain toxic compounds[].

Botanical References

Range

Coasts of the Indian Ocean from Africa through Arabia, Asia to Australia and New Zealand.

Habitat

Intertidal zone mudflats and sandy shores, and the estuaries and tidal river banks (brackish water). A common and often dominant constituent of mangrove swamps and a pioneer of new mud banks[].

Properties

Conservation Status	Least Concern
Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Evergreen Tree
Height	4.00 m
Pollinators	Insects
Self-fertile	Yes
Cultivation Status	Wild

Cultivation Details

A plant of tropical and subtropical coastal areas, where it is found at elevations up to 50 metres. It grows best in areas where annual daytime temperatures are within the range 20 - 34°c, but can tolerate 8 - 39°c[]. It can be killed by temperatures of -1°c or lower[]. It prefers a mean annual rainfall in the range 1,500 - 2,500mm, but tolerates 1,000 - 4,000mm[]. The plant can also tolerate drier areas with an annual rainfall as low as 200mm[].
Requires a sunny position[, ]. Plants have a wide physiological tolerance to salinity, being able to survive in fresh stagnant water as well as in seasonally dry conditions with very high salinity[]. They tolerate soils with a pH in the range of 6 to 8.5[]. Prefers a pH in the range 6.5 - 7, tolerating 6 - 7.5[].
Very tolerant of heavy metals in the soil[].
Trees suffer little from removal of branchwood because they can resprout rapidly from buds along the stems[].
Honey bees collect nectar from the flowers[].
The seeds start germinating while still attached to the tree, but the embryo stays within the fruit until fruit fall. Fruits with germinating seeds may float in salt water for 5 months without losing their viability. Most of these strand within 1 km of the mother tree, and very few were observed to disperse more than 10 km[].
In many mangrove regions, the potential of Avicennia marina is considered limited and other mangrove species such as Rhizophora spp. Are often more highly valued for timber, firewood, charcoal, dye and tannin production. Although mangroves are often heavily exploited, Avicennia marina is often left[].

Edible Uses

The cotyledons of the seed are occasionally eaten, but may contain toxic compounds[]. They need to be cooked[].

Medicinal

White mangrove is used in traditional medicine. Research has shown that several medically active components are present in the plant including iridoid glucosides, flavonoids and naphthoquinone derivatives[]. Some of these have shown strong antiproliferative and moderate cytotoxic activities as well as antibacterial effects[].

The resin from the bark is used to treat snake bites and to remove the placenta after childbirth[].

In Madagascar a leaf decoction has been used as antidote after eating poisoned fish[].

Leaf and bark decoctions are used as an anodyne and are applied externally against scabies[].

The wood ash has been used to treat skin complaints[].

Aqueous, ethanol and butanol crude extracts of the aerial parts of the plant were tested for antimicrobial activity. The butanol extract was the most effective, followed by the ethanol extract. The aqueous extract had low activity. The butanol extract at 2000 μg/disc had a very good antibacterial activity against both gram‐positive and gram‐negative bacteria as well as moderate to good antifungal activity against Candida albicans and Aspergillus flavus[].

Agroforestry Uses:

The tree is useful for preventing coastal erosion and as a windbreak[].
The tree is often a pioneer in sandy habitats, but may also invade mud flats[].
The tree tolerates heavy metals in the soil very well. The roots may be employed as a biological indicator of environmental exposure to copper, lead and zinc[].

Other Uses

The bark contains tannins[]. The source of a reddish and brown dyes[, ].
The bark has been utilized commercially for tanning, but the tannin content is rather low[].

The smoke of burning wood is considered very efficient as a mosquito repellent[].

The greyish to yellowish wood is heavy and durable with a fine and even texture[]. It is used for poles in house building, for boat construction, especially for the ribs, for furniture and handles, and to make beehives[, ]. The branches serve as stakes for fences[].
The wood is also used as firewood and for charcoal production; it is especially used for lime burning[].

Propagation

Seed - best sown as soon as ripe[]. The seeds are very susceptible to desiccation. There is also progressive deterioration of the internal tissues of the seeds associated with fungal infection during hydrated storage. Young seedlings grow best when they are in contact with fresh water, but growth diminishes soon under these conditions and is best in water with 10 - 50% of full seawater salinity for older seedlings[].
Natural regeneration is often abundant, and wildlings can be collected to serve as planting stock[].
Propagation by air layering and root suckers has been successful[].

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