Eucalyptus

About 600; for a full list, see

Overview

All eucalypts are evergreen, although some species have deciduous bark. An essential oil extracted from eucalyptus leaves contains compounds that are powerful natural disinfectants and which can be toxic in large quantities. Several marsupial herbivores, notably Koalas and some possums, are relatively tolerant of it. The close correlation of these oils with other more potent toxins called formylated phloroglucinol compounds allows koalas and other species to make food choices based on the smell of the leaves. However, it is the formylated phloroglucinol compounds that are the most important factor in choice of leaves by koalas.

Related Topics:
Evergreen - Bark - Essential oil - Marsupial herbivore - Koala - Possum

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On warm days vapourised eucalyptus oil rises above the bush to create the characteristic distant blue haze of the Australian landscape. Eucalyptus oil is highly flammable (trees have been known to explode) and bush fires can travel easily through the oil-rich air of the tree crowns. Eucalypts are well adapted for periodic fires, in fact most species are dependent on it for spread and regeneration: both from reserve buds under the bark, and from fire-germinated seeds sprouting in the ashes.

Related Topics:
Bush - Bush fire - Regeneration

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Eucalypts originated between 35 and 50 million years ago, not long after Australia-New Guinea separated from Gondwana, their rise coinciding with an increase in fossil charcoal deposits (suggesting that fire was a factor even then), but they remained a minor component of the Tertiary rainforest until about 20 million years ago when the gradual drying of the continent and depletion of soil nutrients led to the development of a more open forest type, predominantly Casuarina and Acacia species. With the arrival of the first humans about 50 thousand years ago, fires became much more frequent and the fire-loving eucalypts soon came to account for roughly 70% of Australian forest.

Related Topics:
Australia-New Guinea - Gondwana - Casuarina - Acacia

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The name Eucalyptus means "well-covered"; it describes the bud cap. A small genus of similar trees, Angophora, have also been known since the 18th century. In 1995 new evidence, largely genetic, indicated that some prominent Eucalypt species were actually more closely related to Angophora than to the other eucalypts; they were split off into the new genus Corymbia. Although separate, the three groups are allied and it remains acceptable to refer to the members of all three genera Angophora, Corymbia and Eucalyptus as "eucalypts".

Related Topics:
Angophora - 18th century - 1995 - Genus - Corymbia

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Specimens of the Australian Mountain-ash, Eucalyptus regnans, are among the tallest trees in the world at 92 metres tall (Forestry Tasmania; pdf file), making them the tallest of all flowering plants; other taller trees such as the Coast Redwood are all conifers.

Related Topics:
Eucalyptus regnans - Coast Redwood - Conifer

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Most eucalypts are not tolerant of frost, or only tolerate light frosts down to -3°C to -5°C; the hardiest, are the so-called Snow Gums such as Eucalyptus pauciflora which is capable of withstanding cold and frost down to about -20°C. Two sub-species, E. pauciflora niphophila and E. pauciflora debeuzevillei in particular are even hardier and can tolerate even quite severe continental type winters.

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Several other species, especially from the high plateau and mountains of central Tasmania such as E. coccifera, E. subcrenulata, and E. gunnii have produced extreme cold hardy forms and it is seed procured from these genetically hardy strains that are planted for ornament in colder parts of the world.

Related Topics:
Tasmania - Genetic

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Eucalypts exhibit leaf dimorphism. When young, the leaves are opposite and often roundish and occassionally without petiole. When several years old, the leaves become quite slender and with long petiole. Plants do not flower until adult foliage start to appear, except in E. cinerea.

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The Coolibah tree of Waltzing Matilda is a eucalyptus, E. microtheca or E. coolabah.

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Eucalypts support the larvae of some hepialid moths: Abantiades species feed on the roots; Aenetus species burrow into the trunk.

Related Topics:
Larva - Hepialid - Moth - Abantiades - Aenetus

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