AppearanceGrey mangroves grow as a shrub or tree to a height of three to ten metres, or up to 14 metres 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, five to eight centimetres 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 ; these grow to a height of about 20 centimetres, and a diameter of one centimetre. 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 a centimetre 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.
Grey mangrove is a highly variable tree, with a number of ecotypes, and 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, but is intolerant of shade. A number of botanists have proposed division of the species, but currently three subspecies are recognised:
⤷ ''Avicennia marina'' subsp. ''australasica''
⤷ ''Avicennia marina'' subsp. ''eucalyptifolia''
⤷ ''Avicennia marina'' subsp. ''marina''
DistributionIt is distributed along Africa's east coast, south-west, south and south-east Asia, and Australia. It occurs in New Zealand between 34 and 38 degrees south; its Māori name is ''mānawa''. 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, Oman, as well as in similar environments on both side of the Red Sea , and Qatar and southern Iran along the Persian Gulf coast. It is also found in the mangroves of South Africa where it is one of the two most dominant mangroves. The species is also found in Somalia.
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