Eucalyptus polybractea

Common name: Blue mallee

Other common names: Mallee

Description

Blue mallee is an essential oil-yielding eucalypt originating from inland regions of southern Australia, its natural range extending across semi-arid parts of neighbouring north-west Victoria and south-west New South Wales.

It is typically a multi-trunked tree 5 to 10 m (16 to 32 ft) tall, with the trunks anchored by a large root mass and leaning away from the centre, forming a wide-spreading canopy. The bark is grey-brown and peeling off in long, thin strips that accumulate at the tree's base, leaving behind smooth new bark.

The leaves are typically eucalypt, being sword-shaped, 5 to 8 cm (2 to 3 in) long and dull blue- to grey-green. They are alternately arranged along the stems at the ends of the branches and give off a characteristic eucalyptus oil aroma when crushed.

Flowers are small, with numerous creamy-white filaments set in a cup-shaped base. They are bore in small clusters of between seven and ten, arising at the sides of the branchlets, and come into bloom from early autumn to early winter.

Fertilised flowers develop into small, woody, goblet-shaped seed capsules containing small oval, grey, brown or black seed.


Inglewood, Victoria, Australia

Use

Blue mallee is one of the world's principal sources of Eucalyptus oil, along with Tasmanian Blue gum (Eucalyptus globulus), Broad-leaved peppermint (Eucalyptus dives), Narrow-leaved peppermint (Eucalyptus radiata), Queensland peppermint (Eucalyptus exserta) and Gully gum (Eucalyptus smithii).

The leaves yield on steam distillation, commercial quantities of eucalyptus oil, of the cineole (aka. eucalyptol) type, which is the most valuable of the  Eucalyptus oils because of its medicinal and antiseptic qualities. 

Cineole-type eucalyptus oil is a proven expectorant, antiseptic and antibacterial, particularly against Streptococcus. It is used in cough drops and syrups, vaporiser fluids, ointments, liniments, gargles and oral hygiene products such as toothpaste and mouthwash. It is also commonly used in dentistry, particularly in solvents and sealers for tooth fillings after root canal surgery. 

Cineole type oils are also a good stain remover, having proven effective in removing grease, glue and dried stains from both skin and clothing. Eucalyptus oils, more generally, are used in cleaning, mould removal, disinfecting, perfumery, pharmaceutical, personal care and pest insect control products.

Blue mallee eucalyptus oil is a colourless to pale yellow liquid with a strong but sweet camphorous and fresh-cooling aroma and is similar in taste. 

Around 7000 to 10,000 kg kilograms of fresh leaves can be harvested per hectare, per year, in commercial operations and with an average oil content of 2%, yields 140 to 200 kgs of oil, the equivalent to 125 to 178 pounds of oil per acre. The cineole content ranges from 50 to 80%.

The flowers yield sufficient nectar for honey production and the pure honey is medium amber in colour, medium density, sweet and with a good flavour. Pollen is also yielded in good amounts for brooding honeybees.


General interest

The word 'mallee' in the name 'Blue mallee' derives from an Aboriginal term for the types of small, multi-trunked eucalyptus trees common to semi-arid regions of southern Australia.

Climate

Grows naturally in semi-arid, warm temperate climates, generally areas with annual lows of 8 to 14°C, annual highs of 21 to 25°C, annual rainfall of 400 to 600 mm and a summer dry season of 5 to 7 months, extending to 12 months with irrigation or groundwater.

Growing

Blue mallee is not usually cultivated, with most of the material used for distilling harvested from wild trees. This involves using a heavy roller to crush the natural stands of the trees to encourage new growth that then becomes ready for harvesting in eighteen to twenty-four months.

However, there has been a move to establish Blue mallee plantations in recent years, with the trees planted in rows and then mechanically harvested on an eighteen-month rotation.

Blue mallee grows best on moderate to light, free-draining clay-loam, silt-loam, loam, sandy-loam, loamy-sand and sand soils of a moderately acid to neutral nature, generally with a pH of 5.5 to 7.5, and on sites with full-sun exposure.

Problem features

Prolonged skin contact with eucalyptus essential oil may cause burning dermatitis and blisters in some people and it can be poisonous if ingested in large amounts.

Where it grows

With irrigation or groundwater

References

Books

  • Arctander, S. 1960, Perfume and flavor materials of natural origin, Elizabeth, New Jersey

  • Boland, D. & Brooker, I. & McDonald, M. W. 2006, Forest trees of Australia, 5th ed., CSIRO Publishing (Ensis), Melbourne

  • Brady, G. S. & Clauser, H. R & Vaccari, J. A. 2002, Materials handbook : an encyclopedia for managers, technical professionals, purchasing and production managers, technicians and supervisors, 15th ed., McGraw-Hill, New York

  • Byrne, T. & Bourke, M. & Salvin, S. 2004, The new crop industries handbook, Rural Industries Research and Development Corporation (RIRDC), Canberra, Australia

  • Cribb, A. B. & Cribb, J. W. 1982, Useful wild plants in Australia, William Collins, Sydney

  • Culbreth, D. M. R. 1927, A manual of materia medica and pharmacology : comprising the organic and inorganic drugs which are or have been recognized by the United States pharmacopeia, 7th ed., Febiger, Philadelphia

  • F. R. Beuhne 1922, Honey flora of Victoria, Melbourne Albert J. Mullett, Govt. printer

  • Guenther, E. & Althausen, D. 1948 to 1952, The essential oils (6 volumes), Van Nostrand Publishing, New York

  • Hall, N. 1972, The use of trees and shrubs in the dry country of Australia, Australian Government Publishing Service, Canberra, Australian Capital Territory

  • Khan, I. A. & Abourashed, E. A. 2010, Leung's encyclopedia of common natural ingredients : used in food, drugs and cosmetics, 3rd edition, Wiley Publishing, Hoboken, New Jersey

  • Marcar, N. E. 1995, Trees for saltland : a guide to selecting native species for Australia, Division of Forestry, Commonwealth Scientific and Industrial Research Organisation (CSIRO) Australia, Canberra

  • McIlroy, R.J. 1963, An introduction to tropical cash crops, Ibadan University Press, Ibadan, Nigeria

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