Eucalyptus smithii

Common name: Gully Gum

Other common names: Gully ash, Gully peppermint, Blackbutt peppermint, Ironbark peppermint, White top

Description

Gully gum is an essential oil yielding eucalypt originating from south-eastern Australia, its natural range extending from hilly parts of New South Wales, just west of Sydney, south to eastern Victoria.

A tall, handsome tree on favourable sites, it reaches heights of up to 40 m (130 ft) with a straight, slim trunk, slightly buttressed at the base and up to 1.5 m (5 ft) in diameter, supporting a moderately branched, rounded crown. On marginal sites and in open spaces, it is typically 10 to 20 m (32 to 65 ft) tall with a stout trunk and heavily branched crown. The bark is dark brown or grey with vertical cracks and persists on the lower trunk but exfoliates on the upper trunk and branches, revealing smooth, creamy-white under-bark.

As with many eucalypts, the leaves change shape as the tree matures, with noticeable differences on seedling and mature trees. On mature trees, they are narrowly lance-shaped with a slight curve, up to 20 cm (8 in) long, dull green, and give off a eucalyptus aroma when crushed. They are alternately arranged on the stems at the branch ends and remain on the tree in all seasons.

Flowers are small, with numerous creamy-white filaments set in a cup-shaped base. These are borne in small clusters of usually seven, arising at the sides of the branchlets, and come into bloom from summer to early autumn.

Fertilised flowers develop into small, woody, goblet-shaped seed capsules containing tiny, disc-shaped, brown-black seed.

Use

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

The leaves on steam distillation yield 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 are generally used in cleaning, mould removal, disinfecting, perfumery, pharmaceutical, personal care and pest insect control products.

Gully gum eucalyptus oil is a colourless pale yellow liquid with a strong yet sweet camphorous and fresh-cooling aroma and is similar in taste. The cineole content ranges from 70 to 80%.

From 5000 to 8000 kg kilograms of fresh leaves are harvested per hectare, per year, in Southern African commercial plantations. And with an average oil content of 2%, yields are 100 to 160 kgs of oil, the equivalent of 89 to 143 pounds of oil per acre. 

Gully gum wood is hard, closely grained and moderately heavy, averaging around 550 kgs per cubic meter (34 lbs per cubic foot). The tree can produce reasonably straight trunks, but the wood often has spiral grain, making it splits badly and difficult to work, limiting its use. It is used infrequently, to a small extent, in construction, such as for fencing. However, it has shown good potential as pulpwood. And it is already cultivated in South Africa for this purpose, being high pulp-yielding, fast-growing and coppicing well, or re-growing strongly after being cut back. It also makes excellent firewood.

Climate

Grows naturally in warm-temperate, subtropical and tropical highland climates, generally areas with annual lows of 7 to 15°C, annual highs of 17 to 26°C, annual rainfall of 600 to 2000 mm, and a dry season of 6 months or less, extending to 12 months with irrigation.

Gully Gum does not thrive in areas where the average high of the warmest month is above 29°C (84°F).

Growing

New plants are usually started from seed, as cuttings do not easily strike roots. The seed can be stored for several years under cool, dry, air-tight conditions.

Performs best on deep, fertile, free-draining clay-loam, silt-loam, loam, sandy-loam and loamy-sand soils of a moderately acid to neutral nature, generally with a pH of 5.0 to 7.0, and on sites with full to partial sun exposure.

In essential oil production, it is managed as a short-rotation coppice crop, with the leaves harvested every twelve months and the harvest planned for completion before the start of new leaf flush.

Problem features

There does not appear to be any record of it anywhere as a weed or invasive species, despite its cultivation outside of its native range, in China, Africa (Central and Southern), South America, Hawaii and New Zealand. It is assessed as a low weed risk species for Florida by the IFAS Assessment of Non-Native Plants in Florida's Natural Areas.

Prolonged skin contact with Eucalyptus essential oil may cause burning dermatitis and blisters in some people. 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

  • Clarke, B. & McLeod, I. & Vercoe, T. 2009, Trees for farm Forestry : 22 Promising Species, Rural Industries Research and Development Corporation (RIRDC), Wagga Wagga, New South Wales

  • Coppen J.J.W. 1995, Flavours and fragrances of plant origin, Non-wood forest products (Volume 1), Food and Agriculture Organization of the United Nations (FAO), Rome

  • 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

  • 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

  • Troup, R.S. & Joshi, H. B. 1975 to 1981, Silviculture of Indian Trees (3 volumes), Government of India Publications, New Delhi

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