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DISPLAYING POSTS TAGGED: xanthorrhea australia (1)

Southern Grasstree

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by Brendan
Publish date
1 April 2012
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Exhibition horticulturalist Brendan Fleming is turning April's Bug of the Month post into Plant of the Month. He is one of the Live Exhibits staff that tend the plants in the Forest Gallery and Milarri Garden.

From an early age I have enjoyed bushwalking within the Grampian Ranges in western Victoria. One particular plant species found there that fascinates me is Xanthorrhoea australis, the Southern Grasstree. X. australis is the most widespread of the genus of 30 odd species and subspecies. It is found down the eastern coast of Australia.

Southern Grasstrees A spectacular display of Southern Grasstrees following a bushfire in the Grampians.
Image: Brendan Fleming
Source: Brendan Fleming
 

Its appearance is unlike any other indigenous plant. Older grasstrees have a blackened, sometimes gnarled elevated trunk, with bluish-green whorled leaves that seem to explode from the crown and drape down to skirt the stem.

The Southern Grasstree is very slow-growing. It grows approximately one to three centimetres per year, reaching a height of three metres in about 100 years. It has a shallow root system and is found in even the poorest of soils. Whilst not generally occurring in areas with less than 250mm rainfall, it does best in areas exceeding 500mm per year. Southern Grasstrees are found in the understorey of woodlands, heaths, swamps, and rocky hillsides.

Grasstree species are mostly distinguished by the shape of their leaves in cross-section. X.australis has a diamond shape, and with the leaves being softer than other species.

apex of a Southern Grasstree Close up of the apex of a Southern Grasstree in Milarri, showing a single diamond-shaped leaf in cross section.
Image: Brendan Fleming
Source: Museum Victoria

From germination it takes about seven years to reach maturity, and although sporadic flowering and fruiting can occur thereafter, X.australis generally flower following fire. It is not well understood why fire stimulates reproduction, but cutting off the leaves can also initiate flowering. Application of ethylene, which is present in smoke, has a similar effect, indicating that flowering is stimulated from a hormonal response to leaf removal.

I found an extraordinary scene following bushfires several years ago in the Grampians National Park. Thousands of flower spikes up to 3m high as far as the eye can see, even curly ones, evoking some Leunig illustration!

Grasstree flower spikes Although most flower spikes are perfectly vertical, I occasionally see odd shapes at the Grampians.
Image: Brendan Fleming
Source: Brendan Fleming

The flowers are highly scented and produce much nectar, prized by birds, mammals and insects which pollinate the flowers. Each stalk can produce up to 10,000 seeds.

Southern Grasstree flower spike Close-up of the Southern Grasstree flower spike showing individual flowers.
Image: Brendan Fleming
Source: Brendan Fleming
 

Southern Grasstrees are quite susceptible to Phytopthora cinnamomi (root rot), often being the first plants to show symptoms. Hence they are a good indicator of the presence of the disease.

Drenching Southern Grasstree roots with Phosphonate Drenching with Phosphonate is a good way to boost the Southern Grasstree's defences against the Cinnamon Fungus Phytopthora.
Image: Chloe Miller
Source: Museum Victoria

Xanthorrhoea australis is not difficult to propagate. Seed germinate readily in just a few weeks, with no pre-sowing treatment required. Just be patient though - growth is very slow. A grasstree I germinated from seed was well-established but still trunkless after 10 years, and made a handsome addition to my garden.

Grasstrees feature heavily in Indigenous culture. Uses include weapons and fire sticks from flower stalks, sweet drinks from flower nectar, and edible leaf bases.

I don't have to go to the Grampians to enjoy grasstrees. The Milarri Garden at Melbourne Museum displays these remarkable plants right in the heart of Melbourne. Exit the Forest gallery to the North terrace and meet Milarri from its western end. It really is a dramatic entrance to the Museum's Indigenous garden.

Grasstrees at the entrance to Milarri Walk Grasstrees at the entrance to Milarri Walk from the North Terrace during autumn.
Image: Brendan Fleming
Source: Museum Victoria
 

References:

Flora of Tasmania

Wrigley, J. & Fagg, M., 1983, Australian Native Plants, William Collins, Sydney, 512pp.

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