What is a grass tree?
Grass trees, scientifically known as Xanthorrhoea, are a plant that belong to the Asphodelaceae family. They can be found in the understorey layers of eucalypt forests and in heathlands. There are 66 species of grass tree and they are only found in Australia.
Grass trees range in height from 1m to 6m tall, with Xanthorrhoea media growing to around 3m. The leaves of the grass tree are long, narrow and stiff.
Grass trees like Xanothorrhoea media develop a ‘trunk’ from old leaf bases stacked on top of each other. When flowering they develop a 2 to 4 metre long spear-like spike that grows out of the middle of the plant. The top of the spike is covered in hundreds of small flowers. Flowering is often stimulated by bushfire.
Where are grass trees found?
Grass trees are native to Australia and found in all states and territories, particularly on the east and west coast. Grass trees grow well in nutrient poor soils and respond to bushfires by flowering profusely. The species found within Field of Mars Reserve is Xanthorrhoea media..
What role do grass trees play in the ecosystem?
Grass trees provide food for birds, insects and mammals that feast on their nectar, pollen and seeds. Beetle larvae and carpenter bees also live within the flower spikes. Small native mammals such as bandicoots can shelter and nest in the ‘skirt’ of leaves around the trunk. This 'skirt' is formed as the leaves fall around the trunk of the grass tree as they age.
Their ability to resprout and quickly produce flowers after a bushfire makes them a life-line for animals living in recently burnt areas
How are grass trees used by Aboriginal Peoples?
The Darug people of Sydney refer to the grass tree as gulgadya.
Grass trees are very important to Aboriginal peoples, they are a highly valued resource with many uses.
The resin, called yakka, found in the base of the tree is mixed with kangaroo droppings and used as a glue to attach tool heads to handles, and can also be used to seal containers, coolamons, for use with water.
The flower stem is used to make spears, often with three or four prongs and barbs glued, using the resin, to the end to create a fishing spear.
The flowers of the grass tree are soaked in water to make a sweet drink and the leaves and roots of some species can be eaten. Seeds are also collected and ground into flour to make damper.
What structural adaptations do grass trees have to their environment?
Most grass trees are adapted to fire. They have a thick coating of dead leaves called a 'skirt', around their base. The skirt acts as insulation to protect the stem from flames and heat. The living growth-point of the grass tree is buried underground and this is covered above by many moist, tightly packed leaf bases. Many species of grass tree are stimulated to flower after exposure to fire. The leaves of the grass trees produce toxic chemicals to deter herbivore from eating them.
Grass trees have a symbiotic relationship with mycorrhiza, a type of fungi, deep within its root system. A symbiotic relationship is one that benefits both the fungi and the grass tree. The fungi increases the grass tree root’s access to water and nutrients in the soil, helping to increase tree growth especially in poor conditions. The grass tree in return supplies the fungi with sugars.
How do grass trees grow and reproduce?
Grass trees are perennial, which means they live for many years. Some species can potentially live for 600 years. They are very slow growing plants, with their “trunks” only growing up to 6cm per year for the taller species. The ‘trunk’ is formed from old leaf bases stacked up on each other and stuck together with their resin.
When the time comes to reproduce grass trees will send up a towering green spear that erupts into thousands of tiny cream flowers. Grass trees are pollinated by a number of different pollinators such as insects, birds and mammals. Once pollinated the flowers form a tough, pointed seed pod that is usually black. Some grass tree flower spikes can produce up to 10000 seeds.
