The Rainbow Eucalyptus - A Beautiful Tree with a Colourful Trunk
The Unusual and Beautiful Rainbow Eucalyptus
The rainbow eucalyptus is an unusual tree with a very beautiful trunk. The trunk periodically sheds a strip of bark, revealing a green layer underneath. The green layer then changes colour. The shedding and colour change happen at different times in different parts of the trunk. In addition, a variety of new colours are produced. The overall effect is lovely and gives the tree its "rainbow" name.
We're used to beautiful colours in the flowers and fruits of trees and in their autumn leaves, but a coloured trunk is an oddity. The rainbow eucalyptus is greatly admired and is often planted deliberately, either for its colours or for its other benefits. It's an interesting and impressive tree.
Eucalyptus Trees and Shrubs
All eucalyptus trees and shrubs belong to the genus Eucalyptus, which is in the myrtle family, or the Myrtaceae. The trees are native to Australia, Tasmania, New Guinea, Indonesia and the Philippines. Most grow in Australia, which contains hundreds of species of eucalyptus. Eucalyptus trees are very popular and grow as introduced or cultivated plants in many parts of the world.
Koalas and Eucalyptus Leaves
The main component of a koala's diet is eucalyptus leaves. Rumour says that koalas sleep so much due to the influence of the eucalyptus oil in their diet. In reality, the digestion of eucalyptus leaves requires a lot of energy and provides limited nutrition. By sleeping up to twenty hours a day, koalas reduce their energy expenditure.
The rainbow eucalyptus and its relatives have some interesting features. The flowers are unusual and have no petals or sepals. They do have stamens and a pistil, however. The stamens are the male reproductive organs and the pistil is the female organ.
The flower buds take the form of a capsule containing the stamens and pistil. The capsule has a conical lid called an operculum. As a bud matures, the operculum becomes dark and wrinkled. When the bud is ready to open, the stamens expand, pushing the operculum off the top of the capsule. The stamens and the pistil then emerge from the bud. The numerous stamens look like tassels and surround the single, green pistil.
The name "eucalyptus" comes from two Greek words - "eu", which means well, and "calyptos", which means covered. The name refers to the fact that the operculum covers the stamens and pistil.
After pollination and fertilization have taken place, the capsule becomes a woody fruit, which contains the seeds. The fruits are often known as gum nuts (or gumnuts). Pollination is usually carried out by bees.
Eucalyptus Leaves and Oil
Eucalyptus leaves are leathery and hang from the branches. They are often long, narrow and spear-shaped, although some species have wider and more rounded leaves. The leaves contain oil glands.
Some species of eucalyptus produce copious amounts of a volatile and aromatic oil. When a large number of trees grow near each other, the evaporated oil sometimes forms a mist in the air. Eucalyptus oil may have some health benefits, including opening up the airways in people with breathing problems. In addition to being used as a medicine, the oil is used as an insecticide and a fragrance component.
Eucalyptus oil must be sufficiently diluted before use. Concentrated oil can be dangerous if it's taken internally or if it comes into contact with the skin. The active ingredient in the oil is known as eucalyptol or cineol. Eucalyptol is a useful but potentially toxic chemical.
The Rainbow Eucalyptus Tree and its Bark
The rainbow eucalyptus tree (Eucalyptus deglupta) is native to the Philippines, Papua New Guinea and Indonesia. It's also known as the Mindanao gum tree after the island of Mindanao in the Philippines. Gum trees are a group of eucalyptus species which have a smooth bark that is periodically shed.
The multicoloured trunk of the rainbow eucalyptus is a unique and highly appreciated feature. Green, orange, yellow, rusty red, maroon, brown, purple and blue areas may all be visible on the trunk. On some trees the colours are so vibrant and rich that they look artificial. On others the colours have a pastel hue. The colours may be less impressive when the tree is growing outside its native habitat.
The colours of the trunk change as patches or strips of bark in different spots are shed and the underlying area changes from green to another colour. This process also means that no two rainbow eucalyptus trees look the same. The tree is often referred to as a "living work of art".
The Life of a Rainbow Eucalyptus
Like many other eucalyptus trees, the rainbow eucalyptus grows quickly and may become very tall. The mature tree may reach a height of a hundred to a hundred and fifty feet in its native habitat - or even taller - but only sixty to eighty feet in other areas. The mature trunk is six to eight feet in diameter.
The tree produces white flowers and has moderately wide leaves. The leaves produce an oil and release a pleasant scent when crushed. They make much less oil than the leaves of some other species of eucalyptus, though, and aren't used for the commercial production of eucalyptus oil. In the Philippines the rainbow eucalyptus is harvested for pulp wood to make paper.
A Rainbow Eucalyptus Tree
Why Does the Rainbow Eucalyptus Have a Colourful Trunk?
The beautiful and often awesome colours produced by the trunk of the rainbow eucalyptus attract a lot of attention. Very little work has been done to discover why the different colours are produced, however.
Professor David Lee is a botany professor at Florida International University who has explored the production of colour in plants. Based on a brief investigation, he has come up with a tentative theory to explain the colour change in the rainbow eucalyptus tree trunk.
According to Professor Lee, the trunk of the rainbow eucalyptus produces a succession of thin, smooth barks. Each layer of bark is covered by a thin, transparent layer of cells which allows us to see the chlorophyll stored in the cells underneath. Chlorophyll is the green pigment that traps the light energy used in photosynthesis.
As the surface of the trunk ages, the transparent cells on the top of the outermost bark layer become filled with pigments called tannins. Tannins may be yellow, brown or red in colour, depending on the type. The combination of different amounts and kinds of tannins and a reduction in the amount of the underlying chlorophyll may be responsible for the varying colours seen on the trunk of the rainbow eucalyptus.
Tips For Growing a Rainbow Eucalyptus from Seeds
The coloured part of the rainbow eucalyptus bark is eventually shed in strips, revealing a new green layer underneath. The process of tannin accumulation and chlorophyll reduction is then repeated. The shedding of the bark may reduce the growth of plants and parasites on the tree's trunk.
Cultivated Rainbow Eucalyptus
Rainbow eucalyptus trees are an impressive landscaping element. If they're used as an ornamental tree they should be planted in an area where their trunks will remain visible. They need a warm environment and do best in a tropical or subtropical climate. The trees may survive one night of light frost, but they are frost-intolerant plants. Repeated or heavy frost will kill them.
Rainbow eucalyptus is sold as a young tree in a pot or as seeds. The seeds are tiny and may be difficult to handle. In some places rainbow eucalyptus grows in botanical gardens, enabling people to admire the plant without growing their own tree.
There are some drawbacks to growing rainbow eucalyptus. The trees require a lot of water. They can be messy because they frequently shed strips from their bark. They can also reach a large size and take up a lot of space. Furthermore, it's hard to predict how colourful a particular tree will become as it matures. For many lovers of rainbow eucalyptus, however, these disadvantages are no problem. For them, the potential beauty of the tree makes growing one very worthwhile.
© 2015 Linda Crampton