There are about 30 species of Australian Grass trees that belong to the genus Xanthorrhoea. It is a slow growing group of plants that can have a lifespan of up to 600 years. There are many differences between the species with some having a trunk above the ground and can grow up to six metres tall, while others are shorter with their trunks growing below ground.
Many of the mature Grass trees will flower twice to three times a year with rapidly growing flower stalks, which attract a variety of birds and insects that feed on the seeds and flowers. The ancient plants have long been a part of Australia’s flora and because they were threatened from land clearing and exploitation, the species are now protected.
Fortunately, Grass trees are becoming increasingly popular in private gardens and landscaping due to their iconic beauty and low maintenance requirements. Choosing which species to plant is all about personal taste. Some descriptions of the different varieties are provided below.
Xanthorrhoea Acanthostachya is native to South Australia and known as the spiky Grass tree. It has a short trunk with one or two crowns. The leaves are a grey green and shorter than other species, with a prickly flower spike that blooms between August and November.
Xanthorrhoea Australis is also from South Australia and known as the Australian Grass Tree or Kangaroo Tail due to its long, thin, grass-like leaves that grow up to a metre. It can take about 30 years for the leaf tuft to grow above the trunk. This is one of the slowest growing species with a growth rate of no more than two centimetres per year.
Xanthorrhoea Glauca, known as the Grass tree, is widespread in eastern Australia. Its trunk can grow over 5 metres in height and its common to find this species with multiple branches. It makes a unique garden specimen with tall, rod-like flower spikes that rise above the foliage to produce masses of tiny, white flowers.
Xanthorrhoea Gracilis, nicknamed the Slender Blackboy, comes from West Australia. These Grass trees do not form a trunk but has tufted perennial grass growing from branches that form on the stem underground. The leaves grow up to 2 metres with a flower spike that produces creamy white flowers between October and January.
This Western Australian species is a spectacular caudiciform plant with its leaf bases creating a trunk, similar in appearance to that of the cycad. Typically, they are single trunked specimens growing up to 4 metres, although multi-trunk specimens have rarely occurred. The Xanthorrhoea Johnsonii is toxic to cattle that graze on its leaves and its thought that the chemical produced by the plant is a natural deterrent so the juvenile plants can reach maturity.
Xanthorrhoea Macronema is tufted and trunkless with flexible linear leaves that are 1 meter long and rise from the ground. Its long cream flower spike blooms from spring through to summer. This Grass tree is native to Queensland and New South Wales.
Another species found in Western Australian is the Xanthorrhoea Preisii, known as the Western Blackboy. It has an unusual and striking trunk that becomes naturally blackened due to frequent bushfires and flowers in late Winter or early Spring.
Xanthorrhoea Thorntonii is commonly known the Cundeelee Blackboy. These Grass trees are the only species to be found in central Australia, including the Great Sandy Desert, Great Victoria Desert and MacDonnell Ranges. It has a trunk reaching up to 5 metres, topped with perennial grass and a flower spike, which is over one metre and blooms between August and December.