Small tree or shrub up to 9 m high, branches, flower heads and lower surface of leaves greyish or silvery; pneumatophores aerial root specialized for gaseous exchange) are numerous and project from shallow lateral roots.
Leaves: leathery and measure up to 8 cm in length and 5 cm in width. They are oval, pointed and arranged opposite one another on the stems. The leaves are glossy green above with a distinctive pale and slightly hairy, grey underside. Stomata (pores) and salt glands are scattered over the entire leaf surface but are more abundant on the underside.
Flowers yellow or golden. Flower clusters dense, arranged at the tip; flower stalks angular, 10–25 mm long. Outer flower whorl (calyx) 2.5–3 mm long.
Fruit capsule pale green, flattened, 20–30 mm diam.; seed solitary, germinating before fruit falls to allow for quick establishment once the seed settles.
Phenological events in the Grey Mangrove are considered site specific.
Flowering generally occurs in mid to late summer and progressively later in higher latitude sites. In northern parts of Australia, flowering occurs November and December. In southern parts of Australia, flowering generally occurs May and June.
Fruit matures during February to March in most locations, sometimes maturing in August along the Brisbane River. The pale green, flattened fruits (3 cm long and 2 cm wide) consist of a thin, hairy seed coat and enclose two closely folded seed leaves. The seeds germinate while attached to the tree (vivipary), which allows for quick establishment once the seed settles.
As a pioneer species, grey mangrove is very tolerant of extreme saline conditions as it actively resists the uptake of salt at the roots. Grey mangroves can also withstand short periods of inundation by freshwater or hypersaline water.
What to Observe
First fully open single flower
Full flowering (record all days)
End of flowering (when 95% of the flowers have faded)
ClimateWatch Science Advisor
Mangroves are important trees, playing a significant role in providing food and resources for people and animals, protecting coasts, and storing huge amounts of carbon. Rising sea surface temperature, heatwaves and sea level rise from climate change threaten this important species.
With climate change, we expect plants to start shooting and flowering earlier in the year as a result of climate change warming the Earth. They may also start appearing in new areas, as warmer temperatures enable them to live in environments that were previously too cold or unsuitable. They may also die from conditions exceeding their natural tolerances, like the mangrove forests of northern Australia did in 2017 (see links to articles below).
Help scientists answer the question: "How are our animals, plants and ecosystems responding to climate change?"
When To Look
Year-round for germinating seeds that may fall on sand and mud banks. Flowering occurs in mid to late summer.
Note: ClimateWatch is looking for any changes in the timing of these events so remember to keep a lookout all year!
Where To Look
Occurs in intertidal zones on a range of soft muds to sandy soils. It is common along the tidal margins of estuaries and along saline or brackish river areas where it may grow with river, red and other mangrove species. As a pioneer species, grey mangrove commonly colonises developing mud banks. Keep an eye out for seedlings too!
Note: ClimateWatch is looking for any changes outside of their known ranges so remember to keep a lookout beyond these regions too!
Did You Know?
- Avicennia marina is the most common and widespread mangrove found along the mainland coast of Australia.
- This mangrove is traditionally used to treat sting-ray and stonefish ‘stings’ (Milingimbi); ringworms, sores and boils (Yirrkala); scabies (general); 'cheeky' mangrove worm medicine for coughs (Tiwi)