Rainbow Eucalyptus

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.

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.