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Avicennia marina ssp. australasica (Walp.) J.Everett 1994
pronounced: av-ih-SEN-ee-uh mar-EE-nuh subspecies aw-strah-LAY-see-kuh
(Acanthaceae – the black-eyed Susan family)
common name: Grey Mangrove
Avicennia was named for Avicenna – Ibn Sina (980-1037), a Persian physician-philosopher. He is one of the foremost philosophers of the golden age of Islamic tradition. He is also known as al-Sheikh al-Rais (Leader among the wise men), a title that was given to him by his students. In the west he is also known as the ‘Prince of Physicians’ for his famous medical text The Canon of Medicine. In Latin translations, his works influenced many Christian philosophers, most notably Thomas Aquinas. The Canon of Medicine was used as a text-book in most mediaeval universities; in the universities of Montpellier and Louvain it was still being used in 1650.
Avicennia marina is the most widely distributed species of mangrove in Australia, mainly due to its tolerance of cool conditions. On the east coast it occurs as far south as Cromer Inlet in Victoria, while on the west coast it occurs down to Bunbury. In northern Australia it is commonly found on the seaward edge of the mangroves, but it can be found in almost all mangrove environments.
The grey mangrove is a small tree or shrub growing to about 10 m in height. As with other Avicennia species, it has aerial roots (pneumatophores); 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. Our subspecies has light green leathery leaves, 3.5-12 cm long, 1–4 cm wide, the apex acute or sometimes obtuse or acuminate, the base cuneate, the margins entire, the upper surface usually glabrous, and the lower surface greyish or silvery, hairy, and the petiole 5–10 cm long.
The cymes are dense, either in upper axils or arranged in terminal panicles; the peduncles angular, 10–25 mm long. The calyx is 2.5–3 mm long; the corolla white, turning golden-colour; the tube is 1–2 mm long, and the lobes 3–4 mm. The plant flowers for most of the year, especially October to April.
The fruits are compressed capsules, about 3 cm in diameter.
This is a food plant for the caterpillars of a number of Lepidoptera, including:
• the Dull Jewel Hypochrysops epicurus;
• the moth Cenoloba obliteralis;
• the Teak Defoliator Hyblaea puera;
• the Emperor Moth Syntherata janetta;
• the Castor or Croton Caterpillar Achaea janata, and
• the Copper Jewel Hypochrysops apelles.
Locally, plants of this species are often found with leaf galls, home to the larvae of a fly (Diptera), who develop and pupate in the gall.
Although it is not a member of the Rhizophoraceae, Avicennia marina has developed a certain degree of viviparity, referred to as cryptovivarity, where the embryo grows out of the seed coat, but does not emerge from the fruit. 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 heartwood is pale, hard, and tough with a lamellated figure due to alternate bands of two different types of woody tissue. The tree was a great favourite with the Aboriginal inhabitants, who used it for making shields, due to its great resistance to splitting when struck by a spear or other weapon. They also used it for making digging sticks, spears and boomerangs. It was also much used by early colonial settlers in Australia for boatmaking, due to its light weight and its strength; it had been used for many centuries in East Africa to make ribs for Arab dhows, although the early settlers probably didn’t know that. Other East African uses include poles for house building, for furniture and tool handles, and for making beehives. The branches serve as stakes for fences. The wood is also used as firewood and for charcoal production. In colonial Australia, the wood was much sought after to use in burning oyster shells for the production of lime for mortar. The timber, like that of many mangroves, is resistant to termites.
The leaves are quite palatable to cattle, and the plants are sometimes grazed to a low shrub-like form.
The flowers can be a minor source of honey for beekeepers, and a medium source of pollen. Although the honey is not very suitable for commercial production, it is a good source of bee food.
The seeds formed quite an important part of the food supply for some coastal aboriginal tribes. They also boiled up a mixture of bark and leaves in water to make a salve for drying up sores; and ash from burnt branches was used to treat encrusted sores and itchy skin complaints.
Information about medicinal qualities of plants, or about their use as medicines, is for interest only, and is not intended to be used as a guide for the treatment of medical conditions.
Photographs taken in Geoffrey Bay 2009, 2010, Picnic Bay 2016
Page last updated 19th July 2018