As is clearly and succinctly explained in the brilliant books by Mary E. White, ‘The Greening of Gondwana’, ‘After the Greening the Browning’ and ‘Listen Our Land is Crying’, Australia’s foremost paleobotanist details how the Australian island, an “ark” of plants and animals, set out on a journey of discovery and evolution when the Australian land mass separated during the Early Tertiary Period, some 66 million years ago. No longer connected to the land masses we identify as Antarctica, India, Africa, and South America our plants and animals began to take on an increasingly unique form and appearance.
There were no eucalypts present before this time, they evolved over the next 30 million years from the vegetation present and adapted to a myriad of changing climates and land habitats as the island rotated and moved north eastwards to its present location. As Mary says “Evolution within Australia during that time was from the Gondwanan stock, and the individuality of the modern flora and fauna is directly attributable to this fact.”
Genetics and evolution was to give Australia an amazing gift with, eventually, 80% of all plant species and 30% of the genera being endemic, occurring only in Australia. But it was the huge impact of the “omnipresent genus Eucalyptus” that created the “special character and uniqueness of the Australian flora”.
Ultimately around 1,000 species of Eucalyptus evolved across the continent in that time. The overall picture of the genus Eucalyptus changed in the mid 1990’s when Prof. Laurie Johnson persuaded the International Board of Nomenclature to accept his research that the genus should be spilt with his introduction of the genus Corymbia, which included the iconic bloodwoods, ghost gums and spotted gums. In all some 113 species of Eucalyptus were reclassified as Corymbia species. That aside, from the earliest colonial times botanists have been fascinated with the eucalypts and much has been researched, written and generally documented about the Southern Hemisphere horticultural giant.
Interestingly little to no reference is made to any eucalypts in those early writings to any gum trees growing elsewhere; Stan Kelly in his excellent ‘Eucalypts’ volumes, makes reference to the “Anpupu, Eucalyptus urophylla growing on the island of Timor and other Indonesian islands from Wetar to the eastern part of Flores.” And its successful introduction to “Brazil in 1943.”
One entry in Stan’s book refers to “Kamarere (E. deglupta) “ occurring outside of Australia being “scattered from Papua New Guinea and New Britain to parts of Indonesia and the Philippine Islands.” It is clear from this entry that Eucalyptus deglupta is a tropical species enjoying very high rainfall up to 3500mm “but in some years 5000mm.” Unusually it exists happily at sea level on river flats and up to altitudes of 1800m. Considerable reference is then made to its timber qualities and its plantation names in those countries. Nothing is noted about its spectacular bark colours which has earnt it the name in the late 20th century of the Rainbow Tree.
In recent years photographs of the Rainbow Tree’s highly colourful bark have appeared on the internet but skeptics accusing the striking images of being visually enhanced or ‘photo shopped’. Its distinctive bark colours range from purple, blue, orange and maroon and lush green as the bark peels off annually. But with all such stories there is a degree of truth to be found. The images were always referred to as being Hawaiian Rainbow Trees and nurseries even appeared on the world-wide-web claiming to have seed for sale.
Over time more details have come to hand with the origins of the tree being claimed to be the rainforests of Mindanao in the southern and eastern island of the Philippine Islands group. Gardeners in Florida, Texas and California have claimed to have successfully grown the Rainbow Tree but all warn of exposure to cold or heavy frost.
It has also been reported that Eucalyptus deglupta does not contain the aromatic oils found in the other 900+ species. Finally in July 2013 I eventually saw this magnificent tree for the first time on the island of Kauai in Hawai’i and can agree with all the descriptions the Rainbow Tree Eucalypt is truly beautiful and the only eucalyptus species occurring naturally in the Northern Hemisphere.
Following my interview on 2GB with Peter Wilson, Senior Botanist with the Royal Botanic Garden, Sydney, regarding the Rainbow Gum Tree, we learnt that it is a very fast growing tropical eucalypt not suited to Sydney's temperate climate but preferring that of TNQ or the tropics of Darwin. While it is still being grown commercially in the tropics for hardwood timber, gardeners have discovered its highly ornamental and colorful bark. When I asked Peter about the governance of a eucalyptus species originating outside of Australia he replied, "There are at least two species native to the islands to our north and fossils found of extinct species of gum tree in other countries including South America."