help_outline Skip to main content
  • 88 Addison Avenue
    Athelstone SA
    041 849 5834 

Copyright © 2020 All Rights Reserved • Powered by ClubExpress • Terms of UsePrivacy Policy

News / Articles

Meandering Among Eucalypts

Ben Brice | Published on 9/25/2022

Meandering Among Eucalypts

Ray White

The Cazneaux Tree
The Herbig Tree

Eucalypts are seemingly everywhere in Australia, so we tend to take them for granted. They are an old group that date back 50 million years according to the fossil record. The oldest known fossils are impressions of fruits, flowers and leaves that were found sandwiched between layers of volcanic sediments in Patagonia (South America) that was once part of the super continent of Gondwana. (Ref 0). However, the majority of the species have only appeared in the last 2 million years, a mere blink in evolutionary time. During this period the environment warmed as the continent drifted north on its tectonic plate. The oil in the leaves makes eucalypts susceptible to fire and consequently wild bush fires are a natural feature of the landscape. A special trait of most eucalypts is the latent, or epicormic buds that lie beneath the bark. After fire these latent buds sprout and the blackened trunks come to life with green shoots. This is called epicormic regrowth. There are also latent buds in the lignotubers at the base of the trunk that sprout after fire. Further, most eucalypt seeds have a tough coating that survives fire and the seeds respond to smoke chemicals to germinate.

Many eucalypts have greenish chlorophyl-containing tissues in their stems and bark. When sunlight penetrates the outer layer of cells it reacts with the sap (water) with its small quantity of dissolved carbon dioxide to make sugars, starches and release oxygen. This is photosynthesis in the absence of foliage. It allows eucalypts to grow in less-than-ideal climates and recover quickly after fire. All of these facts have enabled eucalypts to adapt to fire and overcome their competition to dominate the landscape. It could be said that eucalypts and fire are symbiotic.

Australia has 92 million hectares of eucalypt forest that makes up three quarters of the native forest area. No other organism in evolution has shown such rapid diversification as the eucalypts. (Refs.1 and 2). They have proven highly adaptable so enabling them to dominate the Australian landscape. They have been able to adapt to a wide range of conditions from tropical summer-rainfall to cool temperate winter-rainfall areas. They grow in both dry and wet (even swampy) locations, sheltered and exposed positions, infertile sands and rich loams and difficult clays, slopes, valleys and hill-tops. In the hot dry deserts and arid areas, they are limited to sheltered depressions where they can collect water or beside watercourses that occasionally flood. On the opposite extreme they survive strong winds, intense cold and even snow at high altitudes in the Alps and in Tasmania. These varying environments have resulted in the trees evolving a wide variety of physical form and shapes.

There are over 900 different Eucalyptus species growing throughout Australia (except for the treeless deserts). Half are found in Western Australia, which is not surprising because the southern half of WA was botanically isolated from the rest of Australia by the desert barrier of the Nullarbor Plain that was once covered by the sea. Our state of South Australia has about 100 species. (WA has 410, NSW 245, Victoria 110, Queensland 230 and Tasmania 35). Eucalypts are also native on our major off-shore islands: Fraser, Melville, Whitsundays, Kangaroo, King and Flinders. There are also a couple of native species in Papua New Guinea, Timor, Java and the Philippines but none are native to New Caledonia or New Zealand (Ref. 3). In addition, there are the sub-species and the hybrids! It makes the botanist hesitant to identify and study all these different species. And then the expert botanists, or taxonomists, or evolutionary botanists go and change a scientific name after discovering its genetic make-up means it does not quite fit in a group. It is a continually evolving and growing field.

The genus (defined as a group of organisms having common characteristics) Eucalyptus was first described and named in 1788 by a French botanist with the pompous name of Charles-Louis L’Héritier de rutelle. The generic name is derived from the Greek eu (well) kalyptos (covered). This refers to the cap, or operculum, that covers the stigma (female parts) and stamens (male flower parts) until it falls away as the flower opens. The first described species was messmate stringybark, Eucalyptus obliqua. It was collected from Bruny Island by David Nelson, a gardener-botanist on Cook’s third voyage. Since 1788 over 900 species, varieties (or sub-species) and hybrids have been discovered and named. (Ref.1)

The common name “eucalypts” includes three botanical genera (plural of genus) that are similar evergreen trees. Eucalyptus is the largest group, Corymbia encompasses the bloodwoods (see later) and Angophora, includes the native apples (that are similar in appearance to the bloodwoods). All eucalypts belong to the myrtle family (Myrtaceae), a large family that consists of more than 3000 species, that is found mainly around the Southern Hemisphere.

Eucalypt common names can lead to confusion if two people from different Australian states talk to each other. A “blue gum” can be several different species; Sydney blue gum, (Eucalyptus saligna), Tasmanian blue gum, (E. globulus) and South Australian blue gum, (E. leucoxylon). The latter is called a “yellow gum” in other Australian states! In Tasmania, E. regnans is called mountain ash and also swamp gum!

Surprisingly the river red gum has already had three scientific names! For many years it was known as E. rostrata and subsequently E. longirostratis. Eventually it was improbably named E. camaldulensis after Camaldoli Hermitage, an Italian monastery in Tuscany. In 1832 a Mr Denhardt took some seeds from Australia back to Tuscany to plant in a nobleman’s garden. Mr Denhardt described the trees in a gardening journal and named them as Eucalyptus camaldulensis. Because he named it first, by the laws of botanical taxonomy this scientific name took priority. Such is science! (The full story is related in Ref.4). Although there are seven sub-species, or varieties, of the river red gums in Australia, our local SA trees are nearly all Eucalyptus camaldulensis sub species camaldulensis that could be considered “the pure strain”. It is always best to refer to the trees by their scientific names to avoid confusion, even though they sometimes change!

Eucalypts are often loosely referred to as “gum trees” because of the gum or kino that exudes from the tree. A number of different types of bark forms have evolved that form the basis of many of the common names. Just by looking at the bark it is possible to start the identification process. All eucalypts add a layer of bark every year and then the outermost layer dies. In smooth bark types (and most young eucalypts have smooth bark), the bark is seasonally shed in flakes, strips or ribbons, usually in mid-summer. As the colour of the bark changes with age and season, the shedding reveals patches and interesting patterns in an attractive range of colours: cream, beige, yellow, grey, brown, jade etc. A tree native to the Philippines is especially beautiful with vivid colours of the rainbow in its trunk and is unsurprisingly called the rainbow gum, Eucalyptus deglupta (Ref 0). Some say the whole genus has the prettiest barks, leaves, fruits and flowers of any woody plant.

In the persistent bark types the outer bark is retained and these are named as stringybarks, ironbarks, boxes and blackbutts etc., according to features of the retained bark. This bark can develop considerable thickness and often splits as the trunk grows in diameter. Stringybark consists of loosely intertwined fibres that can be pulled off in long strips. (Strips of stringybark are so light in weight they can carry embers easily in the wind and light a new spot fire up to 20 km away). Box bark is more adherent, with compact short interlaced fibres that are often tessellated or flaky. Ironbark is rough and infused with resin, becoming hard, dark, and furrowed. Blackbutts, or half-barks, have dark rough persistent bark near the base of the trunk.

There are some other groups that have common names (such as ashes, bloodwoods, peppermints, ribbon gums and scribbly gums) from their bark type that assists with identification. Ashes have fibrous bark on the trunk but smooth bark on the branches. Bloodwood bark is rough and persistent and becomes cracked in rectangular scales or segments. Peppermints have grey fibrous and interlaced bark. Ribbon gums have long thin flat ribbons of bark (E. viminalis is a favourite koala food-leaf source). Scribbly gums are so named because of child-like brown squiggles up and down the trunks that are made by the larvae of moths. Then there are the mallees (multi-stemmed from ground level), mallets, marlocks and yates (from WA)! 

A feature of the adult leaves of almost all eucalypts that is not readily apparent is that they are hairless. The leaves can take many shapes, and they often change as the tree grows. This variation in shapes assists botanists for identification. Their leaves are packed with oil glands that you can see when you hold them up to the light. On a hot day the evaporation of these oils into the atmosphere gives us that very familiar Australian ambience. If it rains after such a hot day, the vapours are condensed and the smell is even more intense. Some species such as Corymbia citriodora smell of lemons while others such as Eucalyptus radiata smell of peppermint. Australians overseas have been known to squash a leaf for a quick whiff of home. 

The flowers have no petals but decorate themselves with many pretty stamens (the male parts). They provide nectar for birds, honeybees, native bees, other insects and some small mammals. Most stamens are white, cream or yellow and are most attractive to insects. But they can also be pink, red, orange, lime and even purple and these colours are more attractive to birds and small mammals. Both native bees and honeybees use the pollen to provide essential protein for growing larvae. Flocks of small birds like weebills and thornbills love to eat the lerps from the leaves. As they flit from leaf to leaf, they make the trees sing with their high-pitched twerps and tweets. The dead hollows make ideal nests for cockatoos and rosellas. The flowering seasons of the various species overlap facilitating hybridisation and the creation of new species.

Eucalypts are the tallest flowering plants on earth. The mighty Mountain Ash (Eucalyptus regnans) found in Victoria and Tasmania is the world’s tallest hardwood and the second tallest tree in the world after the Coast Redwood (Sequoia sempervirens), a conifer in California. There are six other eucalypts in the top fifteen tallest tree species: E. diversicolor, E. globulus, E. viminalis, E. delegatensis,:E. obliqua and E. nitens.  Hence the seven tallest eucalypts are among the world’s tallest fifteen, each capable of exceeding 80m in height. (Note E. obliqua or messmate stringybark is the dominant tree in the wetter parts of the Adelaide Hills)

“In 1884, Bill Cornthwaite and his brother George, were convinced that a regal Mountain Ash (E. regnans) at Thorpdale in Gippsland was the world’s tallest tree. They reasoned there was only one way to prove it – cut it down and measure it. So they did and they were right. The tree was 114.3m tall (or long by this stage) and the brothers claimed the record. Today, a rusting plaque marks the spot of possibly Australia’s most senseless bit of ecological vandalism.” (Ref 5). Our current highest tree is a 100m tall E. regnans in the misty Styx Valley 100km NW of Hobart in Tasmania, named “The Centurion”.

On the other end of the scale, Eucalypt seeds are tiny: about 0.5mm to 1.6mm in diameter. It is amazing that the DNA contained in these small packages results in such large long-lived beautiful organisms.

Eucalypts are the most widely planted trees in the world but are grown mainly in countries such as Portugal, Spain, Italy, southern France, Morocco, Israel, Brazil, Argentina, India and South Africa that have a Mediterranean climate. They are not generally successful in the tropics. Santa Barbara in southern California has over 150 species and the San Francisco Bay Area is notorious for its Tasmanian blue gums (E. globulus) that absorb moisture from its famous fogs through its stomata (leaf openings) resulting in trees that are taller than in their homeland. Some areas in the world such as California have such widespread growth of eucalypts that they are regarded as weeds! The Tasmanian blue gum, E. globulus, is the most widely planted tree in the world (Ref.1).

Grafton Nursery in Worcester in the UK ( has been growing over 60 species for 15 years. They sell them not only to Britain but also all over Europe (for AUD$100 to AUD$200 each). Their catalogue tabulates the characteristics of their 60 trees and notes the minimum temperatures that the various trees can tolerate, something we rarely consider in Australia.  

The river red gum, E. camaldulensis, is found all over mainland Australia (i.e., but not in Tasmania). It is our best-known eucalypt and as such, an iconic tree. Many large old trees have such a wonderful character that it makes them attractive to painters like Hans Heysen. One of its features are the scars left by broken limbs. When stressed by drought the tree can shut off the sap supply to a limb. The weakened limb breaks and drops, often suddenly on a hot day. This loss of a limb to save the remainder of the tree contributes to the tree’s hardiness. Hence the adage ”never park under a red gum”. South Australians have three quite famous river red gums that have achieved the accolade of being recognized in the country’s fifty most remarkable individual trees (Ref 5). 

The first is the venerable “Cazneaux” tree in a dry river-bed about 4 km east of Wilpena Pound in the Flinders Ranges. Harold Cazneaux photographed it in 1937 and named it “The Spirit of Endurance”. It became famous after the photo was published in magazines around the world. It’s still going strong and you can visit it today. 

The second is the famous “Herbig” tree in Springton. This broad squat tree 6 m in diameter (measured 1 m up from the ground) and 25 m tall had its inside burnt out by fire. The hollowed-out middle had an opening facing east away from the wind and rain so it seemed as good a place as any to set up a “home in a hollow” for Johann Herbig and his wife Anna in the late 1850’s. Perhaps it was the fecundity of the tree that enabled the Herbigs to go on to have 16 children, although they did utilise an additional two-room hut nearby. Our early immigrants had a lot of determination to overcome such incredible challenges!  You can visit this tree today. It too is still “going strong” at over 500 years of age. 

The third is east of Mount Torrens. Eons ago, aboriginal people would weave the branches of young trees together to mark places of significance. As the trees grew, the branches fused into “rings” like a three- dimensional net.  Aboriginal elders remember this tree as a border between the Kaurna Adelaide Plains people and the Permangk Murray River people. It was a meeting point for corroborees and celebrations. This tree is hidden away in a valley on private property so unfortunately cannot be visited by the public.

A possible fourth is the Old Gum Tree at Glenelg, famous even though dead and supported by concrete. In 1836 Governor Hindmarsh proclaimed the colony of SA in its shade. 

In the Adelaide Botanic Park near the Zoo are four river red gums that are each more than 400 years old. They stand, silent, scarred and statuesque. Take some time to wander among them today and feel humble. The spirituality of the tree at S-34.91627°, E138.61247° was such that the Salvation Army held its first Australian gathering in its shadow in 1837 (Ref.6). There are also some wonderful isolated examples on the suburban streets of Adelaide (e.g., the corner of Portrush Road and Wootoona Tce.) that were probably too big to cut down during road construction in the early days. Other Australian states also have their iconic old specimens.

The greatest concentration of river red gums lies along the banks of the Murray and Murrumbidgee Rivers, notably in the Barmah Forest east of Echuca. There are a number of sawmills cutting the dense timber into fence posts, railings and railway sleepers where the wood’s high oil content assists resistance to decay.  A mill in Koondrook on the Murray River has been operating continuously since 1889. All sawmills in Australia are regulated by licensed state government foresters. They mark the 5% to 10% of the trees that can be felled from an area called a coupe that is logged every 20 years but leaving mature old growth trees and juveniles to reinstate the grove. This maintains a sustainable resource that is responsibly managed for future generations.

Eucalypts have a multitude of uses: firewood, pulp for paper making, charcoal, furniture timber, floriculture, dyes, oil, windbreaks, soil erosion, removal of carbon dioxide from the atmosphere and didgeridoos. Their possible use for prospecting was only recently discovered in 2013. Eucalypts in the Kalgoolie region of WA have been shown to draw up gold and other metals through their roots and deposit “micro-nuggets” in their leaves and branches. The nuggets are only 8 micro-metres (8x10-6m) in diameter and not worth collecting (mining) but this novel means of locating sub-surface mineral deposits may be exploited in the future. (Ref.1)

Murray Bail wrote a novel entitled Eucalyptus that won the Miles Franklin Award in 1999. It was a story about a man who plants every eucalyptus species on his property. It was probably based on our very own Dean Nicolle who was fascinated by Eucalyptus trees at an early age. He started his specialist arboretum (a garden of trees) when he was 18 years old in 1992 on a tree-less 32-hectare, well-drained sandy loam site near Currency Creek, just north of Goolwa. The rainfall of 450 mm allows temperate species to thrive, yet is low enough to allow desert species to grow. Species from high rainfall areas need supplementary irrigation. This arboretum is the world’s largest collection of eucalypts with about 10,000 trees in cultivation, covering 900 species and every species from SA. You can meander among the eucalypts at an open day free to the general public on Saturday 1 October or Sunday 2 October from 9.00am to 4.30pm. Dean conducts free one hour and extended two hour guided tours at 10am and 2pm on both days. Come and learn more about our famous trees direct from a passionate and practical scientist. 

The Meeting Tree
The Old red gum Saw-mill

River red gum burl (after fire) table and bowl
River red gum firewood plantation in Norton Summit, planted 1985

References and further reading

0.,au/science/Eucalypts are icons of the Australian landscape, but their family tree is shrouded in mystery. A recent article by Genelle Weule.

1. A comprehensive overview of the genus.

2. www.the A 2019 article in The Conversation written by A. Thornhill. One of 30 articles on various aspects of eucalypts written by academics but with easy-to-read journalistic flair.

3. Forest Trees of Australia, by DJ Boland, MIH Brooker, GM Chippendale, N Hall et alia. Fifth edition published in 2006 by CSIRO Publishing. 760 pages. Also available in an e-version. The essential reference of our native trees.

4. River Red Gums and the Tuscan Monks. A fascinating story of how our iconic river red gum came to be named.

5. Australia’s Remarkable Trees by Richard Allen and Kimbal Baker. Published in 2014 by The Miegunyah Press. Of the 50 outstanding individual trees described in this delightful book, 3 are Corymbia and 19 are Eucalyptus. Of these, four are our iconic river red gums with three from SA.

6. Personal communication from John Sandham, Botanic Gardens of SA. John.sandham@sa,

7. Economic Trees and Shrubs for South Australia by Neville Bonney. Published in 1997 by Greening Australia (SA) Inc. 167 pages with one page devoted to each plant with colour photographs. Each page details the areas where it grows, plant uses, soil and rainfall required and management details.

8. A Gardener’s Guide to the Eucalypts by Ivan Holliday and Geoffrey Watton. Published in 1980 by Rigby Publishers. Somewhat dated but the two SA authors include a useful non-botanical key to identifying the eucalypts and a simple guide to the botanical names of the shapes of leaves, flowers and fruits. Each tree has a half page of description, a full-page colour photograph and a half-page colour photo of the fruits, flowers and leaves.

9. Eucalypts of South Australia by Dean Nicolle. Published in 1997 by the author. The origin of the scientific name of each tree is fascinating and helps identification. Each tree is described on one page with the facing page having colour photographs in situ and their buds and flowers. A South Australian map of each tree shows their distribution.

10. Native Eucalypts of South Australia by Dean Nicolle. Published in 2013 by the author as an update of his 1997 book. All known 103 species in SA are covered.

11. Field Guide to Eucalypts by MIH Brooker and DH Kleinig. Published 2006 by Bloomings. Third edition.

12. A gallery of photographs of the arboretum.

Thanks to Dr Andrew Thornhill for reviewing this article.