page_title: Avicennia marina
section_title: Description
hierarchical_section_title: Avicennia marina / Description
caption_attribution_description: Photo taken on the mangrove walk St Kilda, South Australia
context_page_description: Avicennia marina, commonly known as grey mangrove or white mangrove, is a species of mangrove tree classified in the plant family Acanthaceae. As with other mangroves, it occurs in the intertidal zones of estuarine areas.
context_section_description: Grey mangroves grow as a shrub or tree to a height of 3 to 10 m (9.8 to 32.8 ft), or up to 14 m 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 cm (5 in), and a diameter of 1 cm. 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 cm 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 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 number of botanists have proposed division of the species, but currently three subspecies are recognised: 
  A. m. subsp. australasica
  A. m. subsp. eucalyptifolia
  A. m. subsp. marina
caption: Excreted salt on the underside of a Avicennia marina var. resinifera leaf
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