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Xanthorrhoea () is a genus of about 30 species of Succulent plant in the family Asphodelaceae. They are Endemism to Australia. Common names for the plants include grasstree, grass gum-tree (for resin-yielding species), kangaroo tail, balga (Western Australia), yakka (South Australia), yamina (Tasmania, from the palawa kani language), and black boy (or "blackboy"). The most common species is Xanthorrhoea australis, and some of these names are applied specifically to this species.
Flowers are borne on a long flower spike above a bare section called a scape; the total length can be over three to four metres long in some species. Flowering occurs in a distinct period, which varies for each species, and often stimulated by bushfire. Fires will burn the leaves and blacken the trunk, but the plant survives as the dead leaves around the stem serve as insulation against the heat of a wildfire.
The rate of growth of Xanthorrhoea is slow. Some species grow slowly ( in height per year), but increase their rate of growth in response to season and rainfall.
After the initial establishment phase, the rate of growth varies widely from species to species. Thus, while a member of the fastest-growing Xanthorrhoea may be 200 years old, a member of a more slowly growing species of equal height may have aged to 600 years. Many xanthorrhoeas only flower for the first time when they are 100 or more years old.Sean Hogan (2025). 174048097X, Global Book Pub. Pty. Ltd.. 174048097X
A reference to its yellow resin, Xanthorrhoea literally means "yellow-flow" in Ancient Greek. Smith named it, in 1798, from ('yellow, golden') and ('flowing, flow'). The invalid Acoroides ( 'Acorus-like') was a temporary designation in Daniel Solander's manuscript from his voyage with Cook, originally not meant for publication.
Kingia and Dasypogon are unrelated Australian plants with a similar growth habit to Xanthorrhoea. Both genera have, at times, been confused with xanthorrhoeas and misnamed as "grasstrees". Some plant classification systems, such as Cronquist system,Cronquist, A.J. An Integrated System of Classification of Flowering Plants, Columbia University Press, New York 1981. have included a wide range of other genera in the same family as Xanthorrhoea. However, future anatomical and phylogenetic research supported the views of Dahlgren, whom regarded Xanthorrhoea as the sole taxon of the family Xanthorrhoeaceae sensu stricto, which is now treated as a subfamily, Xanthorrhoeoideae.
In South Australia, Xanthorrhoea is commonly known as yakka, also spelled yacca and yacka, a name probably fromPeters, Pam, The Cambridge Australian English Style Guide, Cambridge University Press, 1996, p823. the Kaurna language ( Yakko, or alternatively Kurru). The Ngarrindjeri name is Bukkup.
Some of the above names are applied specifically to Xanthorrhoea australis, the most common species.
| + List of Xanthorrhea species in Australia | |||||||||
| X. acanthostachya | D.J.Bedford | · | · | · | · | · | Y | · | |
| X. acaulis | (A.T.Lee) D.J.Bedford | Y | · | · | · | · | · | · | |
| X. arborea | R.Br. | Y | · | · | · | · | · | · | |
| X. arenaria | D.J.Bedford | · | · | · | Y | · | · | · | |
| X. australis | R.Br. | Y | · | Y | Y | Y | · | · | |
| X. bracteata | R.Br. | · | · | · | Y | · | · | · | |
| X. brevistyla | D.A.Herb. | · | · | · | · | · | Y | · | |
| X. brunonis | Endl. in J.G.C.Lehmann | · | · | · | · | · | Y | · | |
| X. caespitosa | D.J.Bedford | · | · | · | · | Y | · | · | |
| X. concava | (A.T.Lee) D.J.Bedford | Y | · | · | · | · | · | · | |
| X. drummondii | Harv. | · | · | · | · | · | Y | · | |
| X. fulva | (A.T.Lee) D.J.Bedford | Y | Y | · | · | · | · | · | |
| X. glauca | D.J.Bedford | Y | Y | Y | · | · | · | · | |
| X. gracilis | Endl. in J.G.C.Lehmann | · | · | · | · | · | Y | · | |
| X. johnsonii | A.T.Lee | Y | Y | · | · | · | · | · | |
| X. latifolia | (A.T.Lee) D.J.Bedford | Y | Y | · | · | · | · | · | |
| X. macronema | F.Muell. ex Benth. | Y | Y, Fraser Island | · | · | · | · | · | |
| X. malacophylla | D.J.Bedford | Y | · | · | · | · | · | · | |
| X. media | R.Br. | Y | · | · | · | · | · | · | |
| X. minor | R.Br. | Y | · | Y | · | Y | · | · | |
| X. nana | D.A.Herb. | · | · | · | · | · | Y | · | |
| X. platyphylla | D.J.Bedford | · | · | · | · | · | Y | · | |
| X. preissii (syn. X. pecoris F.Muell.) | Endl. in J.G.C.Lehmann | · | · | · | · | · | Y | · | |
| X. pumilio | R.Br. | · | Y | · | · | · | · | · | |
| X. quadrangulata | F.Muell. | · | · | · | · | Y | · | · | |
| X. resinosa (syn. X. hastilis) | Pers. | Y | · | Y | · | · | · | · | |
| X. semiplana | F.Muell. | · | · | Y | · | Y | · | · | |
| X. thorntonii | Tate | · | · | · | · | Y | Y | Y | |
They need fire to clear away dead leaves and promote flowering, as these slow-growing trees were among the first flowering plants to evolve.Ward, D. (2004). Grasstrees show fire history. Australian Geographic, (75),28, Grass trees have developed a structural adaptation which helps the grass tree take advantage of soil fertilized with ash after fire, producing a flowering stalk in the aftermath.
The grass tree forms a relationship with fungi deep in its root system, wherein fungi live in a mutually beneficial relationship with the grass tree roots. The fungus increases the tree root's access to water and nutrients and therefore increases tree growth especially in poor conditions. The grass tree also suffers from a condition known as phytophthora dieback. Phytophthora cinnamomi is a discrete soil borne pathogen that attacks and destroys vascular root systems, causing hosts to perish through lack of nutrients and water. It is spread through infected plants and the movement of contaminated soil and gravel.Parks Victoria. (2016). Cinnamon Fungus. Retrieved from http://parkweb.vic.gov.au/parkmanagement/environment/weeds-and-pests/cinnamon-fungus The leaves of the grass tree are hosts to another fungi, Pseudodactylaria xanthorrhoeae.
Xanthorrhoea is an iconic plant that epitomizes the Australian bush in its ability to live in poor nutrient soils and respond to wildfire.
Commonly-grown species for the garden include Xanthorrhoea australis, X. malacophylla, and X. preissii.
In the bush the flowers could reveal directions, since flowers on the warmer, sunnier side – usually north – of the spike often open before the flowers on the cooler side facing away from the sun.
The resin from Xanthorrhoea plants is used in spear-making and is an invaluable adhesive for Aboriginal people, often used to patch up leaky coolamons (water containers) and even yidaki (). The dried flower stalk scape was also used to generate fire by the hand drill friction method.
On the Tasmanian island of lungtalanana, Aboriginal people use the leaves for weaving.
Resin collected from the plant was used in Australia until the mid-twentieth century for the following purposes:
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