Xanthorrhoea

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"Blackboy" redirects here. For the autobiography, see Black Boy.
Xanthorrhoea
X. semiplana
Scientific classification
Kingdom: Plantae
Clade: Angiosperms
Clade: Monocots
Order: Asparagales
Family: Xanthorrhoeaceae
Subfamily: Xanthorrhoeoideae
Genus: Xanthorrhoea
Sol. ex Sm.
Species

see text

Distribution of Xanthorrhoeaceae s. str.

Xanthorrhoea is a genus of flowering plants native to Australia and a member of family Xanthorrhoeaceae, being the only member of subfamily Xanthorrhoeoideae. The Xanthorrhoeaceae are monocots, part of order Asparagales. There are 28 species and five subspecies of Xanthorrhoea.[1]

Description

The "trunk" of Xanthorrhoea is a hollow ring of accumulated leaf bases. Nutrient transport is via aerial roots that run down the centre.

All are perennials and have a secondary thickening meristem in the stem. Many, but not all, species develop an above ground stem. This is rough-surfaced, built from accumulated leaf-bases around the secondarily thickened trunk. The trunk is sometimes unbranched, some species will branch if the growing point is damaged and others naturally grow numerous branches. Flowers are borne on a long spike above a bare section called a scape, the total length can be up to four metres long in some species. Flowering occurs in a distinct flowering period, which varies for each species. Flowering can be stimulated by bushfire, in which case it occurs in the next flowering period after the fire.

Growth rates

The rate of growth of Xanthorrhoea is very slow. However, this is often generalized to mean they all grow at the rate of about an inch (2½ cm) per year. Actually, after the initial establishment phase, the rate of growth varies widely from species to species. Thus, while a five-metre-tall 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.

Cultivation

Xanthorrhoea may be cultivated, as seed is easily collected and germinated. While they do grow slowly, quite attractive plants with short trunks (10 cm) and leaf crowns up to 1.5 m (to the top of the leaves) can be achieved in 10 years. The slow growth rate means that it can take 30 years to achieve a specimen with a significant trunk. Most Xanthorrhoea sold in nurseries are established plants taken from bushland. Nurseries charge high prices for the plants. However, there is a very low survival rate for nursery purchased plants, which may take 3–4 years to die. The most successful examples of transplanting have been where a substantial amount of soil (> 1 cubic metre) has been taken with the plants.

Common names

The best known common name for the Xanthorrhoea is blackboy. This name refers to the purported similarity in appearance of the trunked species to an Aboriginal boy holding an upright spear. Some people now consider this name to be offensive, or at least belonging to the past, preferring instead grasstree. In the South West, the Noongar name balga is used for X. preissii. In South Australia, Xanthorrhoea is commonly known as yakka, also spelled yacca and yacka, a name probably from a South Australian Aboriginal language,[2] mostly likely Kaurna.

Traditional Aboriginal uses

Xanthorrhoea is important to the Aboriginal people who live where it grows. The flowering spike makes the perfect fishing spear. It is also soaked in water and the nectar from the flowers gives a sweet tasting drink. In the bush the flowers are used as a compass. This is because flowers on the warmer, sunnier side of the spike (usually the north facing side) often open before the flowers on the cooler side facing away from the sun.[3]

The resin from Xanthorrhoea plants is used in spear-making[4] and is an invaluable adhesive for Aboriginal people, often used to patch up leaky coolamons (water-containers) and even yidaki (didgeridoos).

Similar plants

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[5] have included a wide range of other genera in the same family as Xanthorrhoea. However, later anatomical and phylogenetic research has supported the view of Dahlgren[6] who regarded Xanthorrhoea as the sole member of his family Xanthorrhoeaceae sensu stricto, which is now treated as the subfamily Xanthorrhoeoideae of a much more broadly defined family Xanthorrhoeaceae.[7]

Species

5 meter tall Xanthorrhea drummondii in the Avon Valley National Park

According to the World Checklist of Selected Plant Families, as of June 2011 there are 28 species in the genus:[8]

  • Xanthorrhoea australis flower spike, flowering

  • Flower spike, after fruiting

See also

  • Kingia – an unrelated genus, but of similar appearance

References

  1. ↑ Bedford, D. J. (1986). "Xanthorrhoea", in: A. S. George, (Ed) Flora of Australia 46:148–169. ISBN 0-644-04356-3.
  2. ↑ Peters, Pam, The Cambridge Australian English Style Guide, Cambridge University Press, 1996, p823. ISBN 978-0-521-57634-5
  3. ↑ Gardening Australia - Fact Sheet: Xanthorrea
  4. ↑ Quantum - Ancient Resin
  5. ↑ Cronquist, A.J. An Integrated System of Classification of Flowering Plants, Columbia University Press, New York 1981. ISBN 0231038801
  6. ↑ Dahlgren, R. M. T. (1980). "A revised system of classification of the angiosperms". Botanical Journal of the Linnean Society 80 (2): 91–124. doi:10.1111/j.1095-8339.1980.tb01661.x. 
  7. ↑ Chase, Mark W.; Reveal, James L.; Fay, Michael F. (2009). "A subfamilial classification for the expanded asparagalean families Amaryllidaceae, Asparagaceae and Xanthorrhoeaceae". Botanical Journal of the Linnean Society 161 (2): 132–6. doi:10.1111/j.1095-8339.2009.00999.x. 
  8. ↑ WCSP (2011). World Checklist of Selected Plant Families. The Board of Trustees of the Royal Botanic Gardens, Kew. Retrieved 2011-06-27 

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