As we come to the end of spring, look up from the footpath or at the park, and you may spot the fiery flowers of the silky oak, Grevillea robusta.
You may already be familiar with grevilleas – perhaps you have low- growing ground cover and shrub species in your garden.
Some people love the brilliant red, yellow, orange or white flowers of grevilleas. They’re also nesting and roosting havens for small native birds, and so people may plant them to attract wildlife.
Of all the grevillias, the silky oak is the one that catches my eye. It’s the largest and tallest of the species, reaching up to 30 metres. They’re now blooming along the east coast and in some inland places – like huge orange light bulbs dominating the skyline.
Strong like oak
Grevilleas have an ancestry older than dinosaurs. They originated on the super-continent Gondwana, and are closely related to banksias, waratahs and proteas.
Today, the 360 species of grevilleas occur in Indonesia and Australia and are a diverse group. Their colourful, distinctive flowers lack petals and instead consist of a long tube known as a “calyx”, which splits into four “lobes”.
Like most other grevillea, silky oak possesses proteoid or cluster roots, which are dense and fine. These roots greatly increase the absorbing surface area and allow plants to thrive in nutrient-deprived soils.
The word “robusta” refers to the fact that the timber is strong like real oak. The freshly split wood has a silky texture, and a pattern and light colour resembling English oak – hence the common name “silky oak”.
Watch out for the cyanide
Grevilleas literally drip nectar, much to the delight of native birds and bees. Aboriginal people enjoyed the sweet nectar straight from the plant or mixed with water — the original lolly water.
But you have to know which species to taste as some, including the silky oak, contain hydrogen cyanide that could make you ill.
Like other grevilleas the silky oak also contains tridecyl resorcinol, which causes an allergic reaction leading to contact dermatitis. The chemical is similar to the toxicodendron in poison ivy.
So when working with silky oaks, you’d be wise to wear gloves, a face mask, protective eye wear (or face shield) and long sleeved clothing. Washing hands and showering at the end of the day is also recommended.
A prized timber
Silky oak timber was widely used in colonial times. Then it was marketed as “lacewood”, and that name persists today among some who use it.
Silky oak veneer was used widely in colonial table tops and other furniture. Over the years, silky oak has also been used to make window frames because it is resistant to wood rot.
Overseas, silky oak timber is still widely grown, in timber plantations and as windbreaks.
But it’s not widely available in Australia, due to low market demand – the allergens and cyanide it contains means people are generally reluctant to work with it. However silky oak is still highly prized by those who make guitars, and wood turners who make bowls and cabinets.
In the garden
Although an evergreen tree, some specimens are almost semi-deciduous, losing most of their foliage just prior to flowering.
Some specimens of silky oak can be a bit scraggly in their canopy form. They can benefit enormously from a bit of formative pruning when they are young, and perhaps some structural pruning from a good arborist as they get older. A little attention at the right time will be amply rewarded with a safe and great looking tree that can live for 150 years or more.
Silky oak is drought-tolerant. In dry times they often flower a bit later than their usual October blooming, providing a big splash of colour in otherwise drab and difficult years.
The trees can be vulnerable to frost when young, but grow well once taller. This makes the silky oak a potential winner as climate change brings warmer, drier weather.
Silky oaks have been declared an environmental weed in parts of New South Wales and Victoria where it grows outside its native distribution range. They’re also considered an invasive or invader plant in Hawaii and South Africa. However Grevillea robustais declining in its natural rainforest/wet forest habitat.
In some cities in China, silky oaks have been planted along roadsides with great success. The tree has also gained the Royal Horticultural Society’s Award of Garden Merit for its performance in growing under United Kingdom conditions. That just shows you how one person’s weed is another’s treasure.
But as I learn more about First Peoples’ plant knowledge, I’m also better understanding the broader Australian community’s failure to recognise the depth and breadth of our expertise.
Aboriginal people, our culture and deep knowledges are often seen as “in the past”, fixed and stagnant.
Damaging perceptions which cast us as lesser and posit us as a
homogenous peoples, who were limping towards inevitable extinction before
the arrival of a “superior” race, still abound. Such tropes deny our dynamic place in the present day, and our ability to continuously adapt and innovate.
Below I’ve listed five of my favourite indigenous plants and the multiple ways Aboriginal people used them, and continue to do so.
Spiny-headed mat-rush is a large tussocky plant found throughout southeastern Australia.
The Wurundjeri people particularly favour this plant for weaving cultural items such as necklaces, headbands, girdles, baskets, mats and bags for carrying foods, as well as for making technologies such as eel traps and hunting nets.
Its seeds are high in protein. They can be collected and pounded into a bread mix, with the core of the plant and the base of the leaves eaten as a vegetable.
Many diverse Aboriginal peoples use the roots to treat bites and stings. The caterpillars of several butterflies, such as the Symmomus Skipper, also rely on this plant for food and habitat.
2. Wallaby grass
There are around 30 types of wallaby grass in Australia. Native grasslands were once the most extensive habitat of Victoria’s western plains, but are now the most endangered plant community.
Grasslands provide food and habitat for a huge diversity of fauna, particularly birds, such as the peregrine falcon, whistling kite and Australian kestrels. Many animals, such as the legless lizard, little whip snake and fat-tailed dunnart, were once commonplace, but are now scarce in this endangered ecosystem.
Wallaby grass seeds make an excellent bread by pounding them into flour. The leaves and stem are also used to make cultural items, such as nets for fishing and hunting.
It’s also incredibly hardy – highly tolerant to frost, heat and drought, and requiring no fertilisers and little water. And it makes an excellent lawn, controlling erosion and weeds.
3. Bulbine lily (Bulbine bulbosa)
In summer, bulbine lily dies back to a dormant bulb, before re-shooting in late autumn. In spring, it displays vibrant yellow flowers.
Bulbine lilies can be found in all states except Western Australia, growing wild in tandem with milkmaids and chocolate lilies in the few areas of Victoria’s undisturbed remnant vegetation.
It’s considered the sweetest tasting of all edible root plants and is available year-round. You can find a plump, round, cream-coloured storage organ (a type of underground stem) under its stalk, which can be eaten after being roasted. Bulbine lily is also nutritious, a good source of calcium and iron.
4. Black kurrajong (Brachychiton populneus)
Aboriginal peoples from many diverse groups favour the fibrous kurrajong bark for making string for fishing lines, nets and bags, as well as body adornments such as headbands.
Flowers turn to fruit in the form of leathery pods. These pods contain highly nutritious yellow seeds, which contain around 18% protein and 25% fat, and high levels of magnesium and zinc.
To eat the seeds, you first must remove toxic yellow hairs surrounding them. They can be eaten raw and roasted, and have a pleasantly nutty flavour. The young roots of this tree also make an excellent food source and can provide water.
5. Black sheoak (Allocasuarina littoralis)
Favouring dry conditions, black sheoak is native to Queensland, Tasmania, NSW and Victoria, and can grow up to eight metres high. It flowers in spring, with either rusty-brown spikes or red flowers that develop into cones.
Its seeds are an important food source for many native birds, including parrots and cockatoos.
Diverse groups of Aboriginal peoples use sheoaks for various purposes. The shoots and cones can be eaten, and sheoak wood can be used to fashion boomerangs, shields, clubs and other cultural implements because the wood is both strong and resists splitting and chipping.
In fact, the earliest evidence of boomerangs, found in the Wyrie Swamp in South Australia, were made from various sheoak species, and were dated at 10,000 years old.
With a mischievous smile, Damien Wright gives the exhibit an unceremonious kick. The enormous, curved slab of river red gum rocks back and forth on the gallery floor, casting a wavering shadow over the “Do Not Touch” sign at its base.
A couple of anxious visitors shuffle over to investigate as Damien tells me how he made this wobbling wooden bowl, and why he chooses to work with the hardest, most challenging timbers.
The river red gum (Eucalyptus camaldulensis) once grew on the banks of the Murray River. Damien discovered the thick slab in a miller’s yard in Wodonga, where it had lain exposed to the elements for years, slowly warping in the heat. What others had dismissed as damaged wood, Damien saw as creative possibility: he relished the opportunity to work with wood that had been “cooked, cured and crazed by the sun”.
In his workshop in Northcote, Melbourne, he worked to accentuate the warp in the wood by curving the edges of the slab, creating a long, bowing channel, almost three metres in length and over a metre wide. Like all his work, this object is an argument he has made with his hands.
The rough, red, cracking grain of the wood runs lengthways across the piece, like gullies and rivulets spreading across a parched, burnt land. Damien encourages this comparison with his title, which is a pointed commentary on the mistreatment of the waterways on which the tree grew.
“It’s called Food Bowl”, he tells me. And then, gesturing to a knot in the centre, “It drains in the middle”.
For Damien, wood is a way of thinking about place and time — even deep time. A river red gum may grow for anywhere between 400 and 1,000 years before it falls. And as it decomposes over centuries it becomes a home for new life. Murray cod lay their eggs in drowned red gums.
To work with wood is to think beyond a human lifespan. When you look at something like the Murray-Darling system from the perspective of a grand old red gum, you see the fragility and inter-connectedness of the waterway, and how rapidly it has degraded with recent human interventions.
“And if you have that conversation about deep time in this country”, says Damien, “you have to talk about Indigenous people and this continent as an occupied and cultural space, not just a physical place”.
River red gums were a part of Australia’s environment long before people arrived here. They grew beside the Murray River when it was a wide, cold, fast-flowing stream; they witnessed its transformation in the late Pleistocene into a narrow, sinuous, seasonal river; and they have remained, over the past 13,000 years, as the water has slowed and warmed, forming swamps, low sand dunes and small lakes along the channel, and seasonal wetlands in the wider riverine plain.
These mighty trees have also been absorbed into the social and cultural worlds of Indigenous Australians. Their roots have been dug and hollowed out to create bowls, their bark cut to craft canoes, and their limbs burned to warm camps and cook food. In recent millennia, they presided over the most densely populated areas of the continent.
Damien tells me how he seeks to evoke this deep history through his craft as he shows me two of his other pieces: a striking lantern (Black Lighthouse) he made in collaboration with Yolngu craftsman Bonhula Yunupingu, which glows like a fire through thin, black wood; and an elegant reading chair and angular side table called Ned — a riff on Sidney Nolan’s Ned Kelly helmet, which it closely resembles.
Each piece of furniture has been made from red gum in a stage preliminary to fossilisation. The wood is black and almost as hard as stone. It is known as ancient red gum.
While other native timbers enable Damien to explore relationships with the Australian environment, the ancient red gum opens a conversation about deep time on this continent.
Geomorphologist Jim Bowler was the first to identify the material as red gum; he used radiocarbon dating to place its age at about 8,000 or perhaps 10,000 years old. Later I call him and, over the phone, he sketches out the wood’s journey from the banks of the Murray River to the workshops of inquisitive artisans like Damien.
The tree would have seeded after the end of the last ice age, at a time when sea levels were rising and the climate was warming.
The rapid snowmelt in the Victorian Alps caused the mountains to shed huge amounts of gravel, which was then swept into the Murray River. As red gums fell into an ancient channel they were covered by this new gravel, which sealed them in the riverbank.
Preserved from decay by the acidity of the water, the entombed wood slowly absorbed enormous amounts of iron and silica. This oxidising and ebonising process is what makes it black through to the centre and hard, much harder than other red gum.
Articulating a future
Jim first became aware of the red gum when he received some samples at the Melbourne Museum in 1990. The damp and fibrous wood had been unearthed in a quarry on Yorta Yorta land in Wodonga, where it was regarded as a nuisance by those more interested in the gravel around it.
Jim and his wife Joan Bowler recognised the significance of the timber and were eager to see it preserved and used. They helped arrange for the director of the museum to provide “authentications” for woodworkers to make it into furniture, and Joan and her friend Annetine Forell travelled the country over the following two decades, drawing the remarkable material to the attention of millers and craftspeople.
The late Kelvin Barton, a miller, woodworker and seventh-generation farmer, became a crucial intermediary. He collected the ancient red gum in Wodonga, reducing its water content in his ersatz kiln to turn it into workable timber. This was how Damien, a long-term friend and collaborator, came to encounter the ancient red gum — indeed it was in Kelvin’s yard that he found the much younger slab that became Food Bowl.
Damien uses the ancient red gum to articulate his vision for Australia. He sees craftsmanship as a language: a practice that is refined over time to communicate knowledge, beauty and ideas.
He considers his furniture — in its functionality as well as its elegance — as an embodiment of this philosophy. Objects tell stories. They become part of our everyday lives and express everyday futures:
My argument is that to take a material that is ten thousand years old and to articulate that in a beautiful and passionate way and to make that a relevant thing to our lives or to peoples’ lives is a way of articulating a future for this continent. It’s a way of understanding our place in time. It’s a way of dealing with people. It’s a way of projecting forward.
Joan Bowler shares this vision for the ancient timber. In 2008, her company Australian Ancient Redgum donated a six-metre “Fossil Tree” to the Children’s Garden at the Royal Botanic Gardens Victoria, so that “children can sit under this ancient tree and look up through the hollowed out centre and dream of what was and what might be”.
Trees that were seeded after the end of the last ice age, that survived the ruptures of invasion and industry, have reemerged to offer a deep-time perspective of the continent.
It is a scale that reveals the long-term costs of short-term exploitation, and renders processes like the degradation of the Murray-Darling river system into sudden events.
Ancient red gum also invites a longer view of Australian history. And in the hands of Joan and Damien, it calls for the acknowledgement of cultures and histories that for so long have gone unrecognised.
From Tasmania’s majestic forest giants to the eucalypt on your nature strip, trees in Australia are many, varied and sometimes huge. But how many are there exactly? And how does their number change over time?
To answer such questions, we mapped changes in Australia’s tree cover in detail, using 30 years of satellite images. We published the results in a recent paper and made the data available for everyone in our new TreeChange web interactive.
Perhaps surprisingly, it turns out that since 1990 we’ve been gaining trees faster than we are losing them. On average, we’ve been gaining eight “standard trees” per year for every Australian.
In total, we found there is currently the equivalent of 1,000 standard trees for every Australian. But this doesn’t mean all our forests are doing well.
There are 24 billion standard trees in Australia
Counting trees is difficult, as there are always more small trees than big ones. So we defined a “standard”: imagine a gum tree with a trunk 30 centimetres in diameter, standing about 15 metres tall.
It’s the sort of good-sized tree you might find in your street or backyard — not huge, but not small either. It might have been planted 15 or 20 years ago. Cut it down and let it dry out, and it will weigh about half a ton.
By this definition, we gained a staggering 28 million hectares of forest over the last 30 years, plus another 24 million hectares of woodland.
So where did they come from, and why wasn’t it reported in the news? Probably because most of the trees were already there. They just grew larger and denser, and crossed the threshold of our definition of a forest, so were counted in.
And are eight new trees each year, per person, enough to soak up our greenhouse gas emissions? No.
And additional carbon is stored on the forest floor in, for example, logs and branches, as well as under the surface as organic matter. This is worth, perhaps, several more trees of carbon. But it is not clear how safe those carbon deposits are from fire and drought.
Still, if you wanted to set yourself a new year’s resolution, planting those additional 16 trees would be a great start.
Gains and losses
The increasing trend in forest extent has not been smooth — there have been big swings corresponding to wet and dry periods.
For example, the climate of northern Australia has become wetter over the last 30 years, which has helped tree growth. Changes in fire regime and the fertilising effect of our carbon dioxide emissions into the atmosphere may also have played a role.
And just like increased rainfall can help increase the area of forests, drought and bushfire can cause them to disappear.
Bushfires may not remove or even kill most trees, but they can cause enough dieback, scorching or thinning for the vegetation to fall short of the definition of a forest or woodland.
Logging can also cause a patchwork of gains and losses when it goes through cycles of harvesting, regrowth and replanting. And land clearing of native forests still occurs in Australia, such as in the old growth forests of Tasmania, which are vital for native wildlife.
It’s not all good news
While we found the total area and biomass of forests and woodlands has been rising, quality can be more important than quantity when it comes to our ecosystems.
Many things are required to make up a high quality forest, such as a rich understory of perennial species, including grasses and shrubs, and even logs and branches on the ground. These features provide important habitats for many native animals.
Large old trees are also important. Some trees take hundreds of years to reach their greatest size, towering up to 100 meters tall.
These forest giants are an ecosystem in themselves, with birds and tree-dwelling mammals, such as sugargliders, relying on their nooks and crannies. Old growth forests also hold far more carbon than a new forest.
In some cases, a few remaining forests and woodlands are all that’s left of an endangered ecosystem, such as once-abundant box gum grassy woodlands.
Such old or rare forests are difficult or impossible to replace once lost. So creating new forests should never be seen as an alternative for protecting our existing ones.
Spring has arrived, and all over the country the hills and riversides are burnished with the green and gold of Australian wattles, all belonging to the genus Acacia.
It’s a spectacular sight, but not a surprising one as there are about 1,000 Australian species in the Acacia genus ranging from very small shrubs to tall, longed-lived trees. They occur in ecosystems from the arid inland to the wet forests of the east coast.
Wattles have been widely used by Indigenous people for millenia, and celebrated by “Wattle Day” on September 1 for more than a century.
But their lineage may be much older. Australian wattles have relatives in Africa, South America, India and parts of Southeast Asia. This distribution suggests the wattles may have originated in Gondwana before the super-continent fragmented about 180 million years ago.
So let’s take a closer look at what makes these iconic flowers so special.
Don’t blame wattles for your hay fever
Not everyone welcomes the wattles’ golden blooms — many blame wattle pollen for their hay fever or asthma.
However, many species of wattle have aggregated pollen, which means it’s very heavy and tends to fall straight to ground. You have to be virtually under the plant for it to affect you.
They can cause trouble, but it’s more likely your allergy is due to some other inconspicuous plant, such as grass, that you haven’t noticed compared to the bright yellow of the wattles. It’s worth having an allergy test.
While a majority of wattles flower in spring and summer, a significant group — such as the sunshine wattle (A. botrycephala), Gawler Range wattle (A. iteaphylla) and flax wattle (A linifolia) — flowers in autumn and winter. This can give the impression in some places that they’re flowering year-round.
What’s more, many species are hardy, and they can help in the process of taking nitrogen from the air and adding to the soil. That means they can be very handy in ancient, nutrient-poor Australian soils.
Many of the smaller shrub wattles may live for only a decade or so, but some, such as mulga (Acacia aneura) can live for centuries and are crucial to the viability and stability of arid inland ecosystems. They can have surprisingly large and deep root systems for such small shrubs or trees. This is to obtain water, but also binds the soil.
However, mulga-munching horses, cattle and other feral grazers threaten the persistence of mulga-dominated communities. If mulga and other inland Acacia species are lost, the soils can become loose and mobile, which results in stable productive land becoming desert.
By any other name
In the early 2000s, there was fierce debate among plant taxonomists about how closely the African and Australian species were related.
The name “Acacia” rightly belonged to the African group, but because there were so many Australian species that would need to be renamed, Australia was allowed to keep the name “Acacia” in 2011 — much to the chagrin of foreign taxonomists.
This resulted in the genus being divided. Australian wattles stayed as Acacia, but African wattles are now in the genera Vachellia or Senegalia, and those from the middle Americas (around Mexico) are Acaciella and Mariosousa.
The different names reflect long, separate histories and different ecological characteristics. (The name changes rankle still with taxonomists!)
There are also weedy wattles in Australia and elsewhere. Many of us know from hard experience that the splendid ornamental tree, Cootamundra wattle (Acacia baileyiana), can become a weed if it grows outside its very restricted natural range in New South Wales. And Australia’s black wattle (A. mearnsii) is a significant weed in other parts of the world.
It can come as a bit of a blow to know Australia’s floral emblem, golden wattle (A. pycnantha), can be weedy both at home and when it travels abroad (perhaps like some Australians).
Interestingly, most of the Australian wattles lack thorns, unlike their relatives in Africa. In Africa, thorns protect the plants from large mammalian grazers such as giraffes.
Ants love wattles, too
If you don’t like ants, it might be worth checking which species of wattle you have in your backyard, or intend to buy.
Many wattles have a very special relationship with some insects. In Central America, ants penetrate the thorns of Bulls Horn wattle trees and establish their colonies. They then defend the tree against other insects, and if branches of another tree touch the host tree, the ants will cause such damage that the other tree will die back.
In Australia, the relationship between ants and wattles is based on food. The hard wattle seeds have a tasty and oil-rich outgrowth called an “aril”, which is irresistible to some ant species.
The ants harvest the seeds and take them back to their nest, where they’re safe from other hungry grazers until it is damaged by fire or flood and the seeds germinate.
Some wattles, the mulga among them, have little glands at the base of their phyllodes (the modified leaf stalks). These glands secrete a form of sugary syrup that attracts feeding ants. These ants may also protect host trees or perhaps leave the flowers alone to allow a greater seed set to grow.
It’s clear wattles have a lot going for them. They are diverse in number, habit, size, longevity and flowering season — there’s a wattle for every occasion. For all of these great traits, it’s still that green and gold that endears them to Australians.
When it comes to new botanical discoveries, one might imagine it’s done by trudging around a remote tropical rainforest. Certainly, that does still happen. But sometimes seemingly familiar plants close to home hold unexpected surprises.
We recently discovered a new genus of Australian daisies, which we’ve named Scapisenecio. And we did so on the computer screen, during what was meant to be a routine analysis to test a biocontrol agent against a noxious weed originally from South Africa.
The term “genus” refers to groups of different, though closely related, species of flora and fauna. For example, there are more than 100 species of roses under the Rosa genus, and brushtail possums are members of the Trichosurus genus.
This accidental discovery shows how much is still to be learned about the natural history of Australia. Scapisenecio is a new genus, but thousands of visitors to the Australian Alps see one of its species flowering each summer. If this species was still misunderstood, surely similar surprises are still out there waiting for us.
How it began
It all started with a biocontrol researcher asking a plant systematist, who looks at the evolutionary history of plants, to help figure out the closest Australian native relatives of the weed, Cape ivy (Delairea odorata).
Weeds like Cape ivy cause major damage to agriculture in Australia, displace native vegetation and require extensive management. Biological control (biocontrol) is one way to reduce their impact. This means taking advantage of insects or fungi that attack a weed, generally after introducing them from the weed’s home range.
A well-known Australian example is the introduction of the Cactoblastis moth in 1926 to control prickly pear in Queensland and New South Wales. Even today it continues to keep that weed in check.
To minimise the risk of selecting a biocontrol agent that will damage native flora, ornamental plants or crops, it’s tested carefully against a list of species of varying degrees of relatedness to the target weed.
Authorities will approve the release of a biocontrol agent only if scientists can show it’s highly specific to the weed. Assembling a list of species to test therefore requires us to understand the evolutionary relationships of the target weed to other plant species.
If such relationships are poorly understood, we might fail to test groups of species that are closely related to the target.
Our target weed Cape ivy is a climbing daisy that has become invasive in temperate forests and coastal woodlands throughout south-eastern Australia. One of us, Ben Gooden, is researching the potential use of Digitivalva delaireae — a stem-boring moth — for its biocontrol.
We tried to design a test list, but could not find up-to-date information on Cape ivy’s relatives. We already knew it is related to the large groundsel genus Senecio, but we didn’t know how closely. And no genetic data existed for many Australian native species of Senecio.
So, we set out to solve this problem together.
First, we assembled already-published DNA sequences for as many Senecio species and relatives as we could find, and then generated sequences for an additional 32 native Australian species.
We then united all these genetic data into a comprehensive phylogenetic analysis. “Phylogenetics” infers the evolutionary relatedness of organisms to each other.
Hidden in the evolutionary tree
The resulting “evolutionary tree” showed many of the native Senecio species where we expected them to be. More importantly, however, it showed us that Cape ivy is actually quite distantly related to Senecio.
To our surprise, the analysis also placed several Australian species traditionally belonging to the Senecio genus far outside of it, indicating they didn’t belong to Senecio at all and needed to be renamed.
The most interesting group of not-actually-Senecio are five species with leaf rosettes and one (or rarely, a few) flowerheads carried on distinctive stalks.
They’re all restricted to alpine or subalpine areas of south-eastern Australia, and all except one are found only in Tasmania. They turned out to be so unrelated, and so distinct from any other named plant genera, that they have to be recognised as a genus in its own right.
We have now named this new genus as Scapisenecio, after the long flower stalks (scapes) characterising the plants.
The most widespread and common species is Scaposenecio pectinatus, commonly known as the alpine groundsel, which is a familiar sight to hikers and bushwalkers in the Australian mainland alps and the central highlands of Tasmania.
Apart from the excitement of finding a previously undescribed, distinctive genus, these results were also directly relevant to the original purpose of our work: informing a plant list to test possible biocontrol agents.
The traditional misclassification of these species would have misled us about their true relationships. Our new genetic data now allow us to test biocontrol agents on an appropriate sample of species, to minimise risks to our native flora.
It is not often we find that a new, unexpected lineage of plants has existed all along, right in front of us.
Australia is home to some of the world’s most dangerous wildlife. Anyone who spends time outdoors in eastern Australia is wise to keep an eye out for snakes, spiders, swooping birds, crocodiles, deadly cone snails and tiny toxic jellyfish.
But what not everybody knows is that even some of the trees will get you.
Our research on the venom of Australian stinging trees, found in the country’s northeast, shows these dangerous plants can inject unwary wanderers with chemicals much like those found in the stings of scorpions, spiders and cone snails.
The stinging trees
In the forests of eastern Australia there are a handful of nettle trees so noxious that signs are commonly placed where humans trample through their habitat. These trees are called gympie-gympie in the language of the Indigenous Gubbi Gubbi people, and Dendrocnide in botanical Latin (meaning “tree stinger”).
A casual split-second touch on an arm by a leaf or stem is enough to induce pain for hours or days. In some cases the pain has been reported to last for weeks.
A gympie-gympie sting feels like fire at first, then subsides over hours to a pain reminiscent of having the affected body part caught in a slammed car door. A final stage called allodynia occurs for days after the sting, during which innocuous activities such as taking a shower or scratching the affected skin reignites the pain.
Pain is an important sensation that tells us something is wrong or that something should be avoided. Pain also creates an enormous health burden with serious impacts on our quality of life and the economy, including secondary issues such as the opiate crisis.
To control pain better, we need to understand it better. One way is to study new ways to induce pain, which is what we wanted to accomplish by better defining the pain-causing mechanism of gympie-gympie trees.
How does these plants cause pain? It turns out they have quite a bit in common with venomous animals.
The plant is covered in hollow needle-like hairs called trichomes, which are strengthened with silica. Like common nettles, these hairs contain noxious substances, but they must have something extra to deliver so much pain.
Earlier research on the species Dendrocnide moroides identified a molecule called moroidin that was thought to cause pain. However, experiments to inject human subjects with moroidin failed to induce the distinct series of painful symptoms seen with a full Dendrocnide sting.
Finding the culprits
We studied the stinging hairs from the giant Australian stinging tree, Dendrocnide excelsa. Taking extracts from these hairs, we separated them out into their individual molecular constituents.
One of these isolated fractions caused significant pain responses when tested in the laboratory. We found it contains a small family of related mini-proteins significantly larger in size than moroidin.
We then analysed all the genes expressed in the gympie-gympie leaves to determine which gene could produce something with the size and fingerprint of our mystery toxin. As a result, we discovered molecules that can reproduce the pain response even when made synthetically in the lab and applied in isolation.
The genome of Dendrocnide moroides also turned out to contain similar genes encoding toxins. These Dendrocnide peptides have been christened gympietides.
The gympietides have an intricate three-dimensional structure that is kept stable by a network of links within the molecule that form a knotted shape. This makes it highly stable, meaning it likely stays intact for a long time once injected into the victim. Indeed, there are anecdotes reporting even 100-year-old stinging tree specimens kept in herbariums can still produce painful stings.
What was surprising was the 3D structure of these gympietides resembles the shape of well-studied toxins from spider and cone snail venom. This was a big clue as to how these toxins might be working, as similar venom peptides from scorpions, spiders, and cone snails are known to affect structures called ion channels in nerve cells, which are important mediators of pain.
Specifically, the gympietides interfere with an important pathway for conducting pain signals in the body, called voltage-gated sodium ion channels. In a cell affected by gympietides, these channels do not close normally, which means the cell has difficulty turning off the pain signal.
The Australian stinging trees make a neurotoxin that resembles a venom in both its molecular structure and how it is deployed by injection. Taking these two things together, it would seem two very different evolutionary processes have converged on similar solutions to win the endgame of inflicting pain.
In the process, evolution has also presented us with an invaluable tool to understand how pain is caused. The precise mechanisms by which gympietides affect ion channels and nerve cells are currently under investigation. During that investigation, we may find new avenues to bring pain under control.
Environmental scientists see flora, fauna and phenomena the rest of us rarely do. In this new series, we’ve invited them to share their unique photos from the field.
Tasmania’s native forests are home to some of the tallest, most beautiful trees in the world. They provide a habitat for many species, from black cockatoos and masked owls to the critically endangered swift parrot.
But these old, giant trees are being logged at alarming rates, despite their enormous ecological and heritage value (and untapped tourism potential). Many were also destroyed in Tasmania’s early 2019 fires.
Former Greens leader Bob Brown recently launched a legal challenge to Tasmania’s native forest logging. And this year, Forestry Watch, a small group of citizen scientists, found five giant trees measuring more than five metres in diameter inside logging coupes. “Coupes” are areas of forest chopped down in one logging operation.
These trees are too important to be destroyed in the name of the forestry industry. This is why my husband Steve Pearce and I climb, explore and photograph these trees: to raise awareness and foster appreciation for the forests and their magnificent giants.
What makes these trees so special?
Eualypytus regnans, known more commonly as Mountain Ash or Swamp Gum, can grow to 100 metres tall and live for more than 500 years. For a long time this species held the record as the tallest flowering tree. But last year, a 100.8 m tall Yellow Meranti (Shorea faguetiana) in Borneo, claimed the title — surpassing our tallest Eucalypt, named Centrioun, by a mere 30 centimetres.
Centrioun still holds the record as the tallest tree in the southern hemisphere. But five species of Eucalypt also grow above 85 m tall, with many ranking among some of the tallest trees in the world.
It’s not only their height that make these trees special, they’re also the most carbon dense forests in the world, with a single hectare storing more than 1,867 tonnes of carbon.
Our giant trees and old growth forests provide a myriad of ecological services such as water supply, climate abatement and habitat for threatened species. A 2017 study from the Central Highlands forests in Victoria has shown they’re worth A$310 million for water supply, A$260 million for tourism and A$49 million for carbon storage.
This significantly dwarfs the A$12 million comparison for native forest timber production in the region.
Tasmania’s Big Tree Register
Logging organisation Sustainable Timber Tasmania’s giant tree policy recognises the national and international significance of giant trees. To qualify for protection, trees must be at least 85 m tall or at least an estimated 280 cubic metres in stem volume.
While it’s a good place to start, this policy fails to consider the next generation of big, or truly exceptional trees that don’t quite reach these lofty heights.
That’s why we’ve created Tasmania’s Big Tree Register, an open-source public record of the location and measurements of more than 200 trees to help adventurers and tree-admirers locate and experience these giants for themselves. And, we hope, to protect them.
Last month, three giant trees measuring more than 5 m in diameter were added to the register. But these newly discovered trees are located in coupe TN034G, which is scheduled to be logged this year.
Logging is a very poor economic use for our forests. Native forest logging in Tasmania has struggled to make a profit due to declining demand for non-Forest Stewardship Council certified timber, which Sustainable Timber Tasmania recently failed. In fact, Sustainable Timber Tasmania sustained an eye watering cash loss of A$454 million over 20 years from 1997 to 2017.
The following photos can help show why these trees, as one of the great wonders of the world, should be embraced as an important part of our environmental heritage, not turned to wood chips.
It’s not often you get to see the entirety of a tree in a single photo. This tree above is named Gandalf’s Staff and is a Eucalyptus regnans, measuring 84 m tall.
While Mountain Ash is the tallest species, others in Tasmania’s forests are also breathtakingly huge, such as the Tasmanian blue gum (Eucalyptus globulus) at 92 m, Manna gum (Eucalyptus viminalis) at 91 m, Alpine ash (Eucalyptus delegatensis) at 88 m and the Messmate Stringybark (Eucalyptus obliqua) at 86 m.
This giant tree, pictured above, was a Messmate Stringybark that was felled in coupe, but was left behind for unknown reasons. Its diameter is 4.4 metres. Other giant trees like this were cut down in this coupe, many of which provided excellent nesting habitat for the critically endangered swift parrot.
Old-growth forests dominated by giant trees are excellent at storing large amounts of carbon. Large trees continue to grow over their lifetime and absorb more carbon than younger trees.
The tree in the photo above is called Obolus, from Greek mythology, with a diameter of 5.1 m. Names are generally given to trees by the person who first records them, and usually reflect the characteristics of the tree or tie in with certain themes.
For example, several trees in a valley are all named after Lord of the Rings characters, such as Gandalf’s Staff (pictured above), Fangorn and Morannon.
Giant trees are typically associated with Californian Redwoods or the Giant Sequoias in the US, where tall tree tourism is huge industry. The estimated revenue in 2012 from just four Coastal Redwood reserves is A$58 million dollars per year, providing more than 500 jobs to the local communities.
Few Australians are aware of our own impressive trees. We could easily boost tourism to regional communities in Tasmania if the money was invested into tall tree infrastructure.
Scientists have been interested in the flora of New Guinea since the 17th century, but formal knowledge of the tropical island’s diversity has remained limited.
To solve this mystery, our global team of 99 scientists from 56 institutions built the first ever expert-verified checklist to the region’s vascular plants (those with conductive tissue).
We found there are 13,634 formally described species of plants in New Guinea, of which a remarkable 68% are known to occur there and nowhere else. This richness trumps both Madagascar (11,488 species) and Borneo (11,165 species), making New Guinea the most floristically diverse island in the world.
From tarantula-like orchids to giant bananas, here we reveal some of the more mysterious plants on our checklist. Sadly, unsustainable logging and climate change threaten the conservation of many New Guinean species, and we highlight urgent solutions.
New Guinea is a land of evocative contrasts. As the world’s largest tropical island – made up of Papua New Guinea to the east and two Indonesian provinces to the west – its biological diversity spans habitats from fringing mangroves to alpine grasslands.
The flora is diverse, filled with the majestic, stunning, intriguing and bizarre. However, very little is known about the conservation status of many species in New Guinea, which remains relatively unexplored by scientists.
There are the few remaining forests of 60 metres high hoop pine (Araucaria cunninghamii) and klinkii pine (A. hunsteinii), that tower majestically up to 30 metres above the already tall rainforest canopy.
Figs, with their copious sap, are present in diverse forms, from small shrubs to vines, or large canopy trees.
And the strongly irritant black sap of the Semecarpus tree, a distant relative of the American poison ivy, causing severe dermatitis, is something naive botanists must learn to avoid!
Then there’s the Ryparosa amplifolia, a rainforest tree that provides swollen hollow stems for ant colonies to live inside. The tree also produces energy rich “food bodies” – granule-like structures on the leaves that mimic animal tissue and provide the ants with sustenance. In return, the ants act as bodyguards, chasing away insect herbivores, and leaf cleaners.
Some of our most popular foods were domesticated from New Guinea, including sugarcane and bananas. But the giant banana, Musa ingens is a a highlight in montane forests. Its leaves can stretch to a length of 5 metres, the tree can grow more than 20 metres tall, and its fruits are massive.
With more than 2,400 species of native orchid species, New Guinea is one of the most spectacular floral gardens in the world. It includes fascinating species such as Bulbophyllum nocturnum, which is the first and only known example of a night-flowering orchid, and Bulbophyllum tarantula, with appendages that resemble the iconic spider.
An uncertain future
Despite New Guinea’s seemingly high number of plant species, at least 3,000 species remain to be discovered and formally described. This estimate is based on the rate of description of new species in the past decades.
Much of New Guinea, particularly the Indonesian part, has been extremely poorly studied, with very few plant species collected. Even within Papua New Guinea, the distribution of many species is inadequately known. This means our findings should be viewed as a baseline upon which to prioritise further work.
The biggest impact on forest conservation is from logging, both clear-felling and degradation. As land is predominantly under customary ownership, addressing subsistence-related forest loss is a long-term challenge. Climate change adds yet further threats, including increased burning of degraded forest due to drier weather.
This means there’s a high risk of the world losing entire species before they are even known.
To this end, in 2018 the governors of Indonesia’s two New Guinea provinces announced the Manokwari Declaration, a pledge to conserve 70% of forest cover for the western half of the island.
Reversing funding shortfalls and declining engagement
Our work builds on many decades of effort by plant collectors whose countless nights under leaking canvas, grass huts and bark shelters have led to thousands of plant discoveries.
Their stories are astounding. These fearless adventurers have sampled water plants by jumping from helicopters hovering low over Lake Tebera, swam in the Purari River rapids to haul a disabled dugout canoe full of botanists and cargo to safety, and have fallen into beds of stinging plants in the mountains of Wagau without subsequent access to pain relief.
Taxonomy – the discipline of identifying, classifying, and understanding relationships between plants – is the key to unlocking the value of this collecting effort.
But the discipline is suffering from global funding shortfalls and declining engagement. For instance, 40% of our co-authors on this work are 55 years or older.
Future opportunities for botanical research with local New Guineans at the helm is also vital – only 15% of the scientific publications on the New Guinean flora over the past 10 years involved local co-authors.
Improved collaboration between taxonomists, scientific institutions, governments and New Guinean scientific agencies could address these critical urgent priorities.
Undoubtedly, the conservation of New Guinea’s unique flora will be challenging and require work on many fronts that transcend single disciplines or institutions. From what we know already, a world of botanical surprises awaits in the last unknown.
After all, as 19th century naturalist J.B. Jukes wrote:
I know of no part of the world, the exploration of which is so flattering to the imagination, so likely to be fruitful in interesting results […] and altogether so well calculated to gratify the enlightened curiosity of an adventurous explorer, as the interior of New Guinea.