The Eucalyptus (Gum) tree is the most well-known of Australian trees. It is the tree from which the Koala eats, and from its branches the Kookaburra laughs. It also has some very interesting characteristics.
(Images – Wikipedia)
The Eucalyptus tree belongs to the genus of flowering trees and shrubs in the Myrtle family (Myrtaceae) of which there are more than 700 species. Many Eucalyptus trees are also known as Gum trees because of the sap which exudes from any break in the bark. The name ‘Eucalyptus’ comes from the Greek ‘well’ and ‘covered’ in reference to the operculum (bud cap) on the calyx (the outermost whorl of the parts that form a flower) that initially conceals the flower.
The majority of the species are native to Australia, with only 15 found outside of Australia (New Guinea, Indonesia and the Philippines). Of these 15, only 9 are not found in Australia. The Eucalyptus species is cultivated throughout the tropics and subtropics including the Americas, Africa, China, Europe, the Indian Subcontinent, the Mediterranean Basin and the Middle East.
Tree Forms and Sizes
Eucalyptus trees can be divided up into three main groups; forest trees, woodland trees and mallees. Forest trees are single-stemmed and have a crown which is only a portion of the entire tree. Woodland trees are also single-stemmed although they often branch at a short distance above ground level. Mallees are multi-stemmed from ground level, and may be so low-growing that they’re considered to be shrubs. Eucalyptus tree heights range from small (10 metres – 33 feet) -very tall (over 60 metres – 200 feet).
Some of the more well-known varieties of the Eucalyptus tree can be identified by their particular bark characteristic:
- Box – a thin and short fibred bark which can be broken into thick flakes or plates called tessellations. Areas of this tree reveal a bleached area called mottling
- Ironbark – a hard, rough and deeply furrowed bark (with ridges).The sap (gum) exuded from this tree is dark red or black in colour; the bark itself, light to dark grey or black
- Ribbon – a bark which is shed in long thin pieces; ribbons, firm strips or twisted curls. The bark is usually held in the crown of the tree
- Scribbly – a smooth bark that carries insect trails or ‘scribbles’ caused by insect larva (the Scribbly Gum moth)
- Stringybark – a long fibred bark which can be pulled off in strings. It is usually thick with a spongy texture. The bark can be gray or gray-brown in colour
Some tropical species of the Eucalyptus tree lose their leaves at the end of the dry season although typically Eucalyptus trees are evergreen. Mature trees are usually tall, with plentiful leaf coverage, although their shade is patchy because their leaves hang downwards. The leaves of a Eucalyptus are covered with oil glands, which gives them a waxy looking, glossy green colour. In contrast the leaves of seedlings are often dull and pale grey to bluish green, although this varies according to the species.
The flowers of the Eucalyptus tree are very distinctive; a combination of flowers and fruit capsules called, ‘gumnuts’. The flowers are comprised of numerous fluffy stamens, (the pollen bearing component) and are typically white, cream, yellow, pink or red in colour. When in bud the stamens are enclosed in a capsule (operculum). As the stamens expand, the operculum is forced off away from the cup-like base, displaying the decorative and colourful Eucalyptus tree flowers.
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