Rainbow Eucalyptus: An Unusual Tree With a Multicoloured Trunk
An Unusual and Attractive Tree
The rainbow eucalyptus is an unusual tree with a beautiful trunk. The trunk periodically sheds a strip of bark, revealing a green layer underneath. This 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 appearance or for its other benefits. It's an interesting and impressive tree.
All eucalyptus trees and shrubs belong to the genus Eucalyptus, which is in the myrtle family, or the Myrtaceae. The plants are native to Australia, Tasmania, Papua 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.
The rainbow eucalyptus (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 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 Bark of the Rainbow Eucalyptus
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. People who would like to grow the tree should be aware that the colours are often much less intense 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".
Other Features of the Tree
Like many other eucalyptus trees, the rainbow eucalyptus grows quickly and may become very tall. The mature tree may reach a height of 100 to a 150 feet in its native habitat—or even taller—but only 60 to 80 feet in other areas. The mature trunk is six to eight feet in diameter. The spread of the tree is 60 to 125 feet.
The tree produces white flowers and has moderately wide, evergreen leaves. The leaves contain glands that produce an aromatic oil. They release a pleasant scent when crushed. They make much less oil than the leaves of some other species of eucalyptus, however, and aren't used for the commercial production of eucalyptus oil. In the Philippines, the tree is harvested for pulp wood to make paper.
The flowers of rainbow eucalyptus and its relatives are unusual. They 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.
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.
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.
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. Some species of eucalyptus produce copious amounts of oil, which is volatile as well as aromatic. 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. More research needs to be performed in relation to its possible benefits, however. 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. The concentrated form is 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.
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 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.
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.
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 and where there is lots of room for them to spread up and out as they grow.
The trees need a warm environment and do best in a tropical or subtropical climate. Cultivated plant experts say that they should be planted in USDA Hardiness Zones 9 to 11. The trees may survive one night of light frost, but they are frost-intolerant plants. Repeated or heavy frost will kill them. The trees require a lot of water as well as warmth.
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.
The rainbow eucalyptus may grow as much as three feet in a year. It's said to live from 50 to 150 years and to be deer resistant.
Potential Drawbacks to Growing the Trees
There are some drawbacks to growing the trees. 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. Their widespread roots may damage buildings and roads.
Another problem is that it's impossible to predict how colourful a particular tree will become as it matures. The colours that the trunk develops may be disappointing. Someone who wants to grow a tree should look at the colours that tend to develop in their part of the world, either in real-life specimens or in photos. This doesn't guarantee that their particular tree will develop similar hues, though.
For some lovers of rainbow eucalyptus, the disadvantages of growing their own tree are not a problem. For them, the potential beauty of the tree makes having one on their property very worthwhile.
Questions & Answers
Are the rings of a cross section colorful as well?
Unfortunately, no. The bark of the tree can have beautiful colours, but the inner wood is much like that of other trees and is white in colour. A multicoloured cross section would be an interesting and lovely sight!Helpful 6
At what age do the Rainbow Eucalyptus' bark colors become obvious?
People who grow rainbow eucalyptus in North America say that the trees don’t develop a coloured bark until they are about three years old and the trunk is about two to three inches thick. The time when the colours appear may vary based on the climate and the growing conditions, however.Helpful 9
Can rainbow eucalyptus grow in zones 8b and 9a?
According to the Missouri Botanical Garden, the answer is no. The garden's web page says that the rainbow eucalyptus grows in zones 10 and 11.Helpful 3
How big is the root system of the rainbow eucalyptus?
The rainbow eucalyptus has a spread of up to 125 feet, so it should be planted at least 60 feet away from a building to allow for this spread. Some sources recommend that it be planted at least 40 feet away from a building. 40 feet may be okay, but it’s a little risky. The problem is that there’s no way to know for certain how big a particular tree will grow. If there’s room in a garden, it’s better to allow some extra space in case the tree becomes large, and its roots spread a long distance from the trunk.Helpful 2
I live in a USDA zone 9. We get a couple of snowy and frosty days a year. Would a rainbow eucalyptus likely survive this environment? Is there anything I could do to protect it?
The tree requires a zone 10 or 11 environment, according to the Missouri Botanical Garden. Their website has a "Contact Us" page in the About menu. They offer to help people who have a gardening question. They may be able to tell you how well the tree will do in your area. A local botany expert at a college or university or a plant organization of some kind may be able to help you, too.Helpful 2
© 2015 Linda Crampton