Eucalyptus (From Greek, ευκάλυπτος meaning "well covered") is a diverse genus of trees (and a few shrubs), the members of which dominate the tree flora of Australia. There are more than seven hundred species of Eucalyptus, mostly native to Australia, with a very small number found in adjacent parts of New Guinea and Indonesia and one as far north as the Philippines islands. Species of Eucalyptus are cultivated throughout the tropics and subtropics including the Americas, England, Africa, the Mediterranean Basin, the Middle East, China and the Indian Subcontinent.
Eucalyptus is one of three similar genera that are commonly referred to as "eucalypts," the others being Corymbia and Angophora. Many, but far from all, are known as gum trees in reference to the habit of many species to exude copious sap from any break in the bark (e.g. Scribbly Gum).
Eucalyptus has attracted attention from global development researchers and environmentalists. Outside of their natural ranges eucalypts are both lauded for its beneficial economic impact on poor populations[1][2] and derided for being an invasive water-sucker,[3] leading to controversy over its total impact and future.[4] It is a fast-growing source of wood, its oil can be used for cleaning and functions as a natural insecticide, and it is sometimes used to drain swamps and thereby reduce malaria risk.
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[edit] Description
[edit] Size and habit
A Eucalyptus may be mature as a low shrub or as a very large tree. There are three main habit and four size categories that species can be divided into.
As a generalisation "forest trees" are single-stemmed and have a crown forming a minor proportion of the whole tree height. "Woodland trees" are single-stemmed although they may branch at a short distance above ground level.
"Mallees" are multi-stemmed from ground level, usually less than 10 metres in height, often with the crown predominantly at the ends of the branchlets and individual plants may combine to form either an open or closed formation. Many mallee trees may be so low growing as to be considered a shrub.
Apart from the forest tree, woodland tree, mallee and shrub habits two further tree forms are notable in Western Australia. One of these is the "mallet", which is a small to medium-sized tree, usually of steep branching habit, sometimes fluted at the base of the trunk and often with a conspicuously dense, terminal crown. It is the habit usually of mature healthy specimens of Eucalyptus occidentalis, E. astringens, E. spathulata, E. gardneri, E. dielsii, E. forrestiana, E. salubris, E. clivicola and E. ornata. The smooth bark of mallets often has a satiny sheen and may be white, cream, grey, green or copper.
Another habit category used in Western Australia is the "marlock". This has been variously applied but Brooker & Hopper[clarification needed] (2001) defined the term and restricted the use to describe the more or less pure stands of short, erect, thin-stemmed "trees" that do not produce lignotubers. These are easily seen and recognised in stands of E. platypus, E. vesiculosa and the unrelated E. stoatei. The marlock is distinguished from mallets which are taller and have a characteristic steep branching habit. The origin and use of the term "morrel" is somewhat obscure and appears to apply to trees of the western Australian wheatbelt and goldfields which have a long, straight trunk, completely rough barked. It is now used mainly for E. longicornis (Red Morell) and E. melanoxylon (Black Morrel).
Tree sizes follow the convention of:
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- Small - to 10 metres in height
- Medium sized - 10 to 30 metres in height
- Tall - 30 to 60 metres in height
- Very Tall - over 60 metres in height
