Botanical Name: Avicennia marina
Species: A. marina
*Avicennia alba Blume
*Avicennia intermedia Griff.
*Avicennia mindanaensis Elmer
*Avicennia sphaerocarpa Stapf ex Ridl.
*Avicennia spicata Kuntze
*Sceura marina Forssk.
Common Names: Peara Baine, Grey mangrove or White mangrove
Avicennia marina is distributed along Africa’s east coast, south-west, south and south-east Asia, Australia, and northern parts of New Zealand. It is one of the few mangroves found in the arid regions of the coastal Arabian Peninsula, mainly in sabkha environments in the United Arab Emirates, Qatar,Bahrain, Oman, as well as in similar environments on both side of the Red Sea (in Yemen, Saudi Arabia, Egypt, Eritrea, and Sudan), and Qatar and southern Iran along the Persian Gulf coast. It is a characteristic species of the Southern Africa mangroves ecoregion, and is one of three species present in Africa’s southernmost mangroves, in the estuary of South Africa’s Nahoon River at 32°56?S. The species is also found in Somalia.
Avicennia marina grows as a shrub or tree to a height of 3 to 10 m (9.8 to 32.8 ft), or up to 14 metres (46 ft) in tropical regions. The habit is a gnarled arrangement of multiple branches. It has smooth light-grey bark made up of thin, stiff, brittle flakes. This may be whitish, a characteristic described in the common name. The leaves are thick, 5 to 8 cm (2.0 to 3.1 in) long, a bright, glossy green on the upper surface, and silvery-white, or grey, with very small matted hairs on the surface below. As with other Avicennia species, it has aerial roots (pneumatophores); these grow to a height of about 20 centimetres (7.9 in), and a diameter of 1 centimetre (0.39 in). These allow the plant to absorb oxygen, which is deficient in its habitat. These roots also anchor the plant during the frequent inundation of seawater in the soft substrate of tidal systems. The flowers range from white to a golden yellow colour, are less than 1 centimetre (0.39 in) across, and occur in clusters of three to five. The fruit contains large cotyledons that surround the new stem of a seedling. This produces a large, fleshy seed, often germinating on the tree and falling as a seedling. The grey mangrove can experience stunted growth in water conditions that are too saline, but thrive to their full height in waters where both salt and fresh water are present. The species can tolerate high salinity by excreting salts through its leaves.
The grey mangrove is a highly variable tree, with a number of ecotypes, and in forms closely resembling other species. It has been reported to tolerate extreme weather conditions, high winds, and various pests and diseases. It is a pioneer in muddy soil conditions with a pH value of 6.5 to 8.0, but is intolerant of shade.
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
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.
Edible Uses: The cotyledons of the seed are occasionally eaten, but may contain toxic compounds. They need to be cooked.
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 ?g/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.
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.
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
Known Hazards: The young seed leaves may contain toxic compounds.