Avicennia marina, commonly known as grey mangrove or white mangrove, is a species of mangrove tree classified in the plant Acanthaceae . As with other mangroves, it occurs in the intertidal zones of estuarine areas. It is distributed along the east coast of Africa, throughout south and south-east Asia, and into Australia. In Australia, it extends much farther south than any other mangrove, occurring in every mainland . It also occurs in New Zealand between 34 and 38 degrees South; its Māori name is 'manawa'.
Grey mangroves grow to a height of three to ten metres. It has light-grey bark made up of thin, stiff, brittle flakes. The leaves are thick, five to eight centimetres long, a bright, glossy green on top and white or grey and hairy underneath. As with other ''Avicennia'' species, it has aerial roots ; these grow to a height of about 20 centimetres, and a diameter of one centimetre. 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 species produces a large fleshy seed, often germinating on the tree and falling as a seedling.
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''