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Bluegum trees – well-known immigrants from Australia

The bluegum tree Eucalyptus globulus has become a common sight on many South African ranches and farms but it is now being regarded as a thirsty invader. It is one of more than 700 species of gum tree that occur mostly in Australia. The name Eucalyptus is of Greek origin and consists of the words eu (well) and kalyptos (covered). It refers to the calyx that covers the flowers of this genus. Eucalyptus globulus that has been introduced to South Africa was first described scientifically in 1800 by the botanist Jacques Labillardiere from Recherce Bay in Tasmania, Australia. The name globulus is Latin for a globe and refers to the shape of the fruit.

Eucalyptus shrubs and trees of the family Myrtaceae are almost entirely limited to Australia with only some 15 species occurring in the adjacent regions and with Corymbia and Angophora being related genera. Eucalyptus developed from Gondwana tropical rain forest plants some 35 to 50 million years ago in a land mass that still contained Australia and New Guinea, the last two tectonic plates to break away from Gondwana 66 to 55 million years ago. The current Antarctic Ice Cap only developed some 5 to 15 million years ago. At the time of breaking away from Gondwana, Australia and New Guinea were humid and covered in tropical rain forests because they had been located near the equator 452 million years ago. Over time, Gondwana slowly rotated until Australia and New Guinea were near the South Pole before they broke away to drift north-eastwards towards Indonesia. Some 20 million years ago Australia started to become arid and lose its soil nutrients which led to vegetation that was dominated by Casuarina and Acacia in open forests. When the Australian climate became more arid 15 million years ago Eucalyptus species became the dominant plants in Australia. This process became more advanced in central Australia when the ice sheet over Western Australia started to melt some 5 to 3 million years ago. Because Australia has no effective geographical barriers such as large rivers and great mountain chains to prevent the spread of fire, Eucalyptus species gradually displaced much of the original Gondwana rain forests except in some localized places....

 

References:

Anon. 2012. Eucalyptus regnans. http://en.wikipedia.org.wiki/Eucalyptus_regnans - last modified on 31 December 2012.

Anon. 2013. Eucalyptus. http://www.en.wikipedia.org/wiki/Eucalyptus - last modified on 20 January 2013.

 

By: Prof J du P Bothma

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