Swamp she-oak fact sheet

What is the swamp she-oak?

The swamp she-oak is a tree endemic to the east coast of Australia. They are found along the shorelines and banks of water environments.

The scientific name for the swamp she-oak is Casuarina glauca. The word  Casuarina  is derived from cassowary, referring to similarities between the drooping appearance of she-oak foliage and cassowary feathers.  Glauca  comes from the Greek word ‘glaukos’, describing the blue-green colour of the foliage.

Depending on specific environmental conditions, swamp she-oaks can grow as low-lying shrubs or trees up to 30 metres tall. They can live up to 200 years.

Swamp she-oaks can be identified alongside watercourses by their distinctive needle-like foliage.

What do swamp she-oaks look like?

Swamp she-oaks have trunks with scaly greyish-brown bark and long, thin greyish-green branchlets that hang down. These branchlets, called cladodes, resemble pine needles and are divided into segments.

Even though they are green, the branchlets are not the leaves of the tree. The actual leaves of the swamp she-oak are tiny ‘scales’ that are difficult to see. These scale leaves are less than a centimetre long, tooth-like and arranged in a ring around the joints of the branchlets.

Small scale leaves which encircle the joints in each branchlet are difficult to see with the naked eye.

The needle-like branchlets of swamp she-oaks are called cladodes.

Swamp she-oak bark is rough and scaly. There are often has patches of grey lichen on the bark.

Swamp she-oaks are dioecious, meaning there are separate male and female trees. They can be distinguished by the flowers and fruit produced.

Male trees produce brown flowers that are arranged in long spikes about one to 3 centimetres long at the end of their branchlets, whilst female trees produce clusters of small red flowers. Female trees also produce spiny, woody cones – their fruit – whilst male trees do not produce any fruit.

Male swamp she-oaks produce flower spikes on the end of their branchlets.

Female swamp she-oaks produce clusters of spiky red flowers and woody fruit.

Where are swamp she-oaks found?

Swamp she-oaks can be found along the east coast of Australia, from central Queensland to southern New South Wales.

They grow in or near brackish water along the banks of rivers, estuaries and coastal areas. Brackish means slightly salty.

By stabilising the soil with their roots, swamp she-oaks play an important role in their ecosystem by reducing erosion and maintaining water quality.

Groves of swamp she-oaks can be found along Buffalo Creek in the Field of Mars Reserve.

The extensive root system of the swamp she-oak helps to stabilise river banks.

What animals use swamp she-oaks?

Nodules on the roots of swamp she-oaks are dug up and eaten by small mammals such as long-nosed bandicoots. Bandicoot snout pokes can often be found around the base of these trees in the Field of Mars Reserve.

In autumn, the pollen from the she-oak branchlets attracts insects which then provide food for insect-eating birds such as grey fantails.

In winter, glossy black cockatoos,  yellow-tailed black cockatoos  and  crimson rosellas  can be found feeding on the seeds of swamp she-oaks. Cockatoos will snap the woody cones of the branches and extract the seeds inside while grasping the cones in their claws, whilst rosellas will feed directly from the cones. Red-browed finches will eat seeds on the ground which have fallen after been dispersed from the cones.

Birds such as willy wagtails, magpie larks and butcher birds make their nests in swamp she-oaks.

A female yellow-tailed black cockatoo.

Red-browed finches eat swamp she-oak seeds that have fallen to the ground.

How are swamp she-oaks adapted to their environment?

Swamp she-oaks are allelopathic. Throughout their life cycle they drop large amounts of leaf litter. The fallen branchlets release chemicals into the soil as they decay. These chemicals prevent other plants from germinating, providing swamp she-oaks with a competitive advantage over other plant species.

Swamp she-oak groves lack an understorey due to allelopathy.

Swamp she-oaks are well adapted to survive extreme environmental conditions. They have a particularly high salt tolerance, allowing them to grow in soils that are occasionally inundated by king tides.

Their shallow root system spreads wide and not deep, allowing them to easily absorb water and nutrients from the soil, especially in areas that might flood. In urban environments, these roots can even invade underground water and sewer pipes.

The small, scale-like leaves help the tree tolerate drought by reducing the amount of water lost through transpiration and evaporation.

The woody fruit protects the seeds inside from being eaten by animals and harsh environmental conditions.

Swamp she-oaks can sprout from existing root systems in a process called suckering. This allows swamp she-oaks to take over new areas or regrow quickly after disturbances such as fire.

Small leaves reduce water loss through transpiration and evaporation. The tiny leaves are the at the end of this branchlet.

Woody fruits protect the seeds inside.

How do swamp she-oaks reproduce?

Swamp she-oaks are dioecious, meaning there are separate male and female trees. Like all flowering plants, trees reproduce through pollination.

Reddish-brown branchlets signify pollen production.

Each year, around late autumn, male trees produce pollen from flower spikes at the ends of their branchlets, giving them a reddish-brown appearance. The wind and small pollinators such as bees help carry the pollen from male to female trees.

Pollinated trees produce woody fruit.

When the female flowers are pollinated, they form a fruit that resembles a spiny, woody cone.

Swamp she-oak seeds feature a single wing.

The fruits of the swamp she-oak mature in winter. Inside the fruit are winged seeds that are dispersed by the wind. Swamp she-oaks produce an average of 70 seeds per fruit.

How are swamp she-oaks used by Aboriginal Peoples?

The wood of the swamp she-oak is dense, very hard and strong. Aboriginal Peoples along the east coast of Australia use wood from the branches as firewood and to make a variety of tools including land spears, digging sticks, shields, clubs and boomerangs.

To the Dharawal and Darug Peoples, swamp she-oaks are known as 'babysitter trees'. This is because they provide a safe place for mothers to leave their children while they work. The trees offer shade, the soft carpet of needles is comfortable to sit on and the children are considered safe from snakes who do not like crossing over the bed of she-oak needles. The lack of undergrowth makes it easy for adults to see the children from a distance. When the breeze blows through the trees, it creates a soothing sound that helps lull young children to sleep.

Children were encouraged to use swamp she-oak seed pods as dreamcatchers before taking a nap or sleeping. They would roll the seed pods between their palms to transfer their worries into them. Then, they would place the seed pod nearby while they slept, allowing any bad dreams to be captured in the small openings. In the morning, the seed pod would be discarded.

Swamp she-oak leaf litter provides a comfortable and safe place for children to rest and play.

Related Fact Sheets

More plant fact sheets

• Grey mangrove fact sheet
• Paper bark tea tree fact sheet
• Bracken fern fact sheet
• Grass tree fact sheet

Habitats and environments with swamp she-oaks

• Field of Mars Reserve fact sheet
• Eucalypt forest fact sheet
• Mangrove forest fact sheet
• Coastal salt marsh fact sheet

Animals that use swamp she-oaks

• Yellow tailed black cockatoo fact sheet
• Crimson rosella fact sheet
• Magpie lark fact sheet
• Long nosed bandicoot fact sheet

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