Botany

Trees of Australia the Tasmanian Blue Gum



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Eucalyptus globulus or Tasmanian Blue Gum belongs to the plant family Myrtaceae or myrtles. A French explorer, Jacques-Julien Houton de Labillardiere first described the tree in 1799. Eucalytus is derived from the Greek words ‘eu’ meaning ‘well’ and ‘kalypto’ ‘to cover’. This refers to the operculum or cap-like structure which covers the top of the bud and falls away when the flower opens.  ‘globulus’ is Latin for ‘a little button’ and pertains to the shape of the fruit.

The fast-growing Tasmanian Blue Gum is a tall, straight tree, typically 30 to 55 metres. Under favourable conditions, it reaches 70 metres high and has a trunk diameter of 2 metres. Young trees may grow two metres a year.

The bark is grey, rough and deeply furrowed forming a ‘skirt’ round the base of the trunk. Past this point, the bark sheds often in strips leaving a smooth surface. The ‘blue gum’ name comes from the colour of the broad young leaves which are a blue-grey colour and have a waxy surface. They appear in opposite pairs and are 6 to 15 cm long.  Once mature, the leaves reach 15 to 35 cm and are sickle-shaped and dark, glossy green with a strong eucalyptus smell. The large flowers (15 to 20 cm diameter) are cream-coloured. Honey from the Tasmanian Blue Gum is quite strongly flavoured.

The Tasmanian Blue Gum occurs in tall, open forest along the east coast and in the south-east of Tasmania. There are isolated pockets on several islands and in the Cape Otway district in southern Victoria.  It prefers a Mediterranean climate with wet winters and summer rainfall. It has been a success in large gardens in Cornwall and has been widely planted as a plantation tree in other parts of the world including New Zealand, South Africa, South America, California and India. Points in its favour are its straightness, rapid growth, adaptability and timber strength.  It is a useful and versatile tree with pale straw to brown timber, often with blue or grey overtones. The grain is open-textured with distinct growth rings.

When properly seasoned, the timber can be used for flooring and surfaces. The timber is used for construction work, telegraph poles, wharf piles, pulpwood and railway sleepers. The Tasmanian Blue Gum supplies 65% of Australian plantation hardwood, most of which is pulped. The Tasmanian Blue Gum is also the world’s primary source of eucalyptus oil with China being the largest commercial producer. The leaves may be used as a herbal tea which is reputed to have therapeutic qualities.

Although once popular as street trees, they have lost favour due to their rapid growth and large size when mature. For these same reasons, they are not commonly grown in household gardens. California is restricting its plantings of the gum as it has shown tendencies to displace native species and, with its high oil content, is considered to contribute to the ferocity of forest fires.

On 27 November 1962, the Tasmanian Blue Gum was proclaimed the floral emblem of the Australian state of Tasmania.


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