Botany

Trees of Australia the Grass Tree



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The unique Grass tree is indigenous to Australia. The taxonomic name is Xanthorrhoea – difficult to say and even more difficult to spell! For many years the plant was called a ‘blackboy’ as the species that develops a trunk is reminiscent of an aboriginal boy holding a vertical spear. This term is now regarded as ‘politically incorrect’ and grass tree has become universally accepted. Other aboriginal names for the plant include balga, yakka or yacca. There are many species of this plant and several subspecies.

Xanthorrhoea is very slow-growing although not as slow as some sources state. They have a lifespan of 600 years. The ‘trunk’ builds over time from an accumulation of leaf bases which form a hollow ring. The leaf bases are held together by a natural resin exuded by the plant. The trunk has a very rough surface. Some species branch naturally, others branch if the growing point is damaged and some don’t branch at all. A long spike of up to four metres may develop from the middle of a ‘skirt’ of long cylindrical spikes. The flowers appear at the top of the spike above a bare section called a scape. There is a flowering season which varies according to the species. Flowering is often stimulated by bushfire. The grass tree is one of the first plants to flower after a fire and supplies badly needed nutrients for birds, bees and insects. The flowers are tiny white to yellow florets which become seed capsules containing hard, black seeds.

The grass tree has a unique root system. The roots are surrounded by microbes called mycorrhiza. The mycorrhiza protects the plant from pests and disease. Grass trees transplanted from their original source often die (though it may take three or four years to do so) because the rootball has been disturbed and the plant lacks the mycorrhiza it needs for its continued survival.

The grass tree is extremely tough and hardy (apart from when it is transplanted without sufficient soil). It favours full sun and good drainage.

It grows only 1 to 2 cm in height per annum. Over time it can grow to over four metres in height. The flowering stalk grows much faster, perhaps 2 to cm per day. Flowering takes place in mature plants every two to three years. The grass tree is favoured by lizards and insects which shelter in the mass of foliage. The flowering spear attracts nectar seeking birds, bees, butterflies and ants.

Uses
Aborigines used the grass tree for many purposes.
*  The light straight stalk was used for the butt of spears.
*  The flower stalk when very dry was easy to light with a drilling stick to produce a fire.

*  Resin collected from the base of the trunk was melted and used for waterproofing bark canoes and water vessels, and/or mixed with other ingredients for form a glue to fix stone spear- and axe-heads to wooden handles
*  The white, tender leaf bases and juicy roots were eaten
*  Seeds were ground to provide a flour
*  Dead leaves in the centre of the plant indicated the presence of edible grubs
*  Carpenter bees build nests in the soft pith of the flower stalk providing globules of honey

Early colonists also used the grass tree for numerous purposes.

*  The burned resin gave a pleasant aroma during church services
*  The resin formed a base for producing varnishes and stove polish. It was also used for sizing paper, and for manufacturing soap and perfume.

Sources:
http://www.abc.net.au/gardening/stories/s1574835.htm


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