Climate change is testing the resilience of native plants to fire, from ash forests to gymea lilies

One year following the 2019/20 fires, this forest has been slow to recover.
Rachael Nolan, CC BY-NC-ND

Rachael Helene Nolan, Western Sydney University; Andrea Leigh, University of Technology Sydney; Mark Ooi, UNSW; Ross Bradstock, University of Wollongong; Tim Curran, Lincoln University, New Zealand; Tom Fairman, The University of Melbourne, and Víctor Resco de Dios, Universitat de LleidaGreen shoots emerging from black tree trunks is an iconic image in the days following bushfires, thanks to the remarkable ability of many native plants to survive even the most intense flames.

But in recent years, the length, frequency and intensity of Australian bushfire seasons have increased, and will worsen further under climate change. Droughts and heatwaves are also projected to increase, and climate change may also affect the incidence of pest insect outbreaks, although this is difficult to predict.

How will our ecosystems cope with this combination of threats? In our recently published paper, we looked to answer this exact question — and the news isn’t good.

We found while many plants are really good at withstanding certain types of fire, the combination of drought, heatwaves and pest insects may push many fire-adapted plants to the brink in the future. The devastating Black Summer fires gave us a taste of this future.

Examples of fire-adapted plants: prolific flowering of pink flannel flowers (upper left), new foliage resprouting on geebung (upper right), seed release from a banksia cone (lower left), and an old man banksia seedling (lower right).
Rachael Nolan

What happens when fires become more frequent?

Ash forests are one of the most iconic in Australia, home to some of the tallest flowering plants on Earth. When severe fire occurs in these forests, the mature trees are killed and the forest regenerates entirely from the seed that falls from the dead canopy.

These regrowing trees, however, do not produce seed reliably until they’re 15 years old. This means if fire occurs again during this period, the trees will not regenerate, and the ash forest will collapse.

This would have serious consequences for the carbon stored in these trees, and the habitat these forests provide for animals.

Southeast Australia has experienced multiple fires since 2003, which means there’s a large area of regrowing ash forests across the landscape, especially in Victoria.

The Black Summer bushfires burned parts of these young forests, and nearly 10,000 football fields of ash forest was at risk of collapse. Thankfully, approximately half of this area was recovered through an artificial seeding program.

Ash to ashes: On the left, unburned ash forest in the Central Highlands of Victoria; on the right, ash forest which has been burned by a number of high severity bushfires in Alpine National Park. Without intervention, this area will no longer be dominated by ash and will transition to shrub or grassland.
T Fairman

What happens when fire seasons get longer?

Longer fire seasons means there’s a greater chance species will burn at a time of year that’s outside the historical norm. This can have devastating consequences for plant populations.

For example, out-of-season fires, such as in winter, can delay maturation of the Woronora beard-heath compared to summer fires, because of their seasonal requirements for releasing and germinating seeds. This means the species needs longer fire-free intervals when fires occur out of season.

The iconic gymea lily, a post-fire flowering species, is another plant under similar threat. New research showed when fires occur outside summer, the gymea lily didn’t flower as much and changed its seed chemistry.

While this resprouting species might persist in the short term, consistent out-of-season fires could have long-term impacts by reducing its reproduction and, therefore, population size.

Out-of-season fires could have long-term impacts on gymea lilies.
Shutterstock

When drought and heatwaves get more severe

In the lead up to the Black Summer fires, eastern Australia experienced the hottest and driest year on record. The drought and associated heatwaves triggered widespread canopy die-off.

Extremes of drought and heat can directly kill plants. And this increase in dead vegetation may increase the intensity of fires.

Another problem is that by coping with drought and heat stress, plants may deplete their stored energy reserves, which are vital for resprouting new leaves following fire. Depletion of energy reserves may result in a phenomenon called “resprouting exhaustion syndrome”, where fire-adapted plants no longer have the reserves to regenerate new leaves after fire.

Therefore, fire can deliver the final blow to resprouting plants already suffering from drought and heat stress.

Drought stressed eucalypt forest in 2019.
Rachael Nolan

Drought and heatwaves could also be a big problem for seeds. Many species rely on fire-triggered seed germination to survive following fire, such as many species of wattles, banksias and some eucalypts.

But drought and heat stress may reduce the number of seeds that get released, because they limit flowering and seed development in the lead up to bushfires, or trigger plants to release seeds prematurely.

For example, in Australian fire-prone ecosystems, temperatures between 40℃ and 100℃ are required to break the dormancy of seeds stored in soil and trigger germination. But during heatwaves, soil temperatures can be high enough to break these temperature thresholds. This means seeds could be released before the fire, and they won’t be available to germinate after the fire hits.

Heatwaves can also reduce the quality of seeds by deforming their DNA. This could reduce the success of seed germination after fire.

Burnt banksia — Many native plants, such as banksia, rely on fire to germinate their seeds.
Shutterstock

What about insects? The growth of new foliage following fire or drought is tasty to insects. If pest insect outbreaks occur after fire, they may remove all the leaves of recovering plants. This additional stress may push plants over their limit, resulting in their death.

This phenomenon has more typically been obverved in eucalypts following drought, where repeated defoliation (leaf loss) by pest insects triggered dieback in recovering trees.

When threats pile up

We expect many vegetation communities will remain resilient in the short-term, including most eucalpyt species.

But even in these resilient forests, we expect to see some changes in the types of species present in certain areas and changes to the structure of vegetation (such as the size of trees).

Resprouting eucalypts, one year on following the 2019-2020 bushfires.
Rachael Nolan

As climate change progresses, many fire-prone ecosystems will be pushed beyond their historical limits. Our new research is only the beginning — how plants will respond is still highly uncertain, and more research is needed to untangle the interacting effects of fire, drought, heatwaves and pest insects.

We need to rapidly reduce carbon emissions before testing the limits of our ecosystems to recover from fire.

Rachael Helene Nolan, Postdoctoral research fellow, Western Sydney University; Andrea Leigh, Associate Professor, Faculty of Science, University of Technology Sydney; Mark Ooi, Senior Research Fellow, UNSW; Ross Bradstock, Emeritus professor, University of Wollongong; Tim Curran, Associate Professor of Ecology, Lincoln University, New Zealand; Tom Fairman, Future Fire Risk Analyst, The University of Melbourne, and Víctor Resco de Dios, Profesor de Incendios y Cambio Global en PVCF-Agrotecnio, Universitat de Lleida

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Planning to plant an Australian native like wattle? Read this first — you might be spreading a weed

Coastal wattle.
Dr David Chael, Author provided

Singarayer Florentine, Federation University AustraliaAustralian native plants are having a moment in the sun, with more of us seeking out and planting native species than in the past. Our gardens — and our social media feeds — are brimming with beautiful Australian native blooms.

But not all Australian native species belong in all Australian environments. In fact, many have become pests in places far from their original homes.

They can crowd out other native endemic species, affect the local balance of insects and other animals, wreck soils and even increase fire risk.

Here are three Australian native plants that have become invasive species after ending up in places they don’t belong.

Sydney golden wattle (Acacia longifolia subspecies longifolia)

Originally extending from East Gippsland in Victoria up about as far as Brisbane in Queensland, this species is undoubtedly photogenic. It’s also an invasive weed in parts of Victoria, South Australia and Western Australia.

It was spread across the nation by well-meaning gardeners who saw it as a charming ornamental plant. However, its seeds made their way into the wild and took off — it’s what’s known in my field as “a garden escapee”.

Like many weeds, this species can capitalise on a natural disaster; after fire it can send out shoots from its base. Acacias are often one of the first species to sprout following a bushfire. They’re now completely dominant and spreading in many areas.

Sydney golden wattle is an invasive weed in other parts of Victoria, South Australia and Western Australia.
Gill Armstrong, Author provided

Seeds of Sydney golden wattle can last in the soil for many decades, long after the parent plants have died. The heat from a fire cracks the hard seed coat, allowing water to enter and germination to take off.

In the Grampians, in Victoria, Sydney golden wattle is causing terrible soil problems. Many native plants endemic to this area don’t like high levels of soil nitrogen, but Acacia longifolia subsp. longifolia is a nitrogen-fixing plant.

Acacia longifolia subsp. longifolia has quite long, thin seed pods.
Gill Armstrong, Author provided

In other words, it increases the nitrogen in the soil and changes the soil nutrient status and even physical aspects of the soil. It can grow tall and produce a lot of foliage, which reduces the amount of light coming to the ground. That makes it harder for native species lower to the ground to survive.

This is a major challenge, especially in biodiversity-rich places like the Grampians.

Coast wattle (Acacia longifolia subspecies sophorae)

The blooms on Acacia longifolia subspecies sophorae (Coast wattle) look more or less the same as many other wattles, but the leaves are a bit shorter and stubbier.

Originally, Coast wattle occurred along the east coast from western Victoria — up about as far as Brisbane and down south as far as Tasmania (where Sydney golden wattle did not occur naturally).

_Acacia longifolia subsp. sophorae_, also known as 'Coastal Wattle', has shorter, stubby leaves. — Acacia longifolia subsp. sophorae, also known as ‘Coastal Wattle’, has shorter, stubby leaves.
Tatters ✾/Flickr, CC BY

It was originally restricted to sandy sites at the top of beaches but has been deliberately planted as a “sand-binder” in other sites. It’s also naturally spread into heathlands inland of the beaches and is now causing huge problems around our coasts.

Like the earlier example, it dominates local ecosystems and displaces native species endemic to the area (particularly in our species-rich heathlands), which affects local insect habitats. It is also now modifying natural sand dune patterns.

It is increasing fire risk by changing heathland plant profiles from mostly short shrubs of limited bulk to tall, dense shrublands with much higher fuel levels.

Coast teatree (Leptospermum laevigatum)

As with Coast wattle, Coast teatree was formerly restricted to a narrow strip on sandy soils just above the beaches of south-eastern Australia. But it has now spread into nearby heathlands and woodlands. It’s even reached as far as Western Australia.

This teatree plant is now considered an invasive species in parts of Victoria and South Australia.

Although the mature plants are usually killed by fire, the seeds are abundant and very good at surviving; they pop out of their capsules after fires.

Coast teatree produces a lot of seeds.
Dr David Chael, Author provided

They are high-density plants that burn quickly in a fire. They are very quick to take over and push out endemic species.

For example, parts of the Wilson’s Prom National Park in Victoria, which was originally a Banksia woodland, have now been converted almost to a teatree monoculture. It is very sad.

A call to action

Authorities are trying their best to keep these and other native invasive species under control, but in some cases things may never go back to the way they were. Sometimes, the best you can hope for is just to strike a balance between native and invasive species.

When you do landcare restoration work or home gardening, I urge you to look up the plant history and see if the species you’re thinking of planting is listed as one that might cause problems in future.

When you go to purchase from a nursery or plant centre, be cautious. Think twice before you bring something into your garden. Too many species have “jumped the garden fence” and now cost us a great deal in control efforts and in native species loss.

Lots of apps, such as PlantNet, can help you identify plants and see what is native to your area.

Australia has spent billions trying to control invasive species and environmental weeds. Anything you can do to help is a bonus.

Singarayer Florentine, Professor (Restoration Ecologist), Federation University Australia

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The 50 beautiful Australian plants at greatest risk of extinction — and how to save them

Caley’s grevillea (*Grevillea caleyi*) occurs in Sydney. It needs fire to germinate but burns are hard to carry out near urban areas.
Tony Auld, Author provided

Jennifer Silcock, The University of Queensland; Jaana Dielenberg, Charles Darwin University; Roderick John Fensham, The University of Queensland, and Teghan Collingwood, The University of QueenslandAs far as odds go, things don’t look promising for the slender-nerved acacia (Acacia leptoneura), a spiky plant with classic yellow-ball wattle flowers. With most of its habitat in Western Australia’s wheat belt cleared for agriculture, it was considered extinct for more than 160 years.

Now, just two plants are known in the world, and they’re not even in the same place. This species is among many Australian plants that have come perilously close to extinction.

To help prevent the loss of any native plant species, we’ve assembled a massive evidence base for more than 750 plants listed as critically endangered or endangered. Of these, we’ve identified the 50 at greatest risk of extinction.

The good news is for most of these imperilled plants, we already have the knowledge and techniques needed to conserve them. We’ve devised an action plan that’s relatively easy to implement, but requires long-term funding and commitment.

What’s driving the loss?

There are 1,384 plant species and subspecies listed as threatened at a national level. Twelve Australian plant species are considered probably extinct and a further 21 species possibly extinct, while 206 are officially listed as critically endangered.

Yellow wattle — Two known plants of slender nerved acacia (*Acacia leptoneura*) remain, about 1 kilometre apart. Propagation attempts have been unsuccessful and the genetic diversity is probably very low.
Joel Collins, Author provided

Australian plants were used, managed and celebrated by Australia’s First Nations people for at least 60,000 years, but since European colonisation, they’ve been beset by a range of threats.

Land clearing, the introduction of alien plants, animals, diseases, and interruptions to ecological processes such as fire patterns and flooding have taken a heavy toll on many species. This is particularly the case in the more densely populated eastern and southern parts of the continent.

Close-up of yellow flower — Ironstone pixie mop (*Petrophile latericola*) occurs on a soil type that’s been heavily cleared for agriculture, and is suspected to be susceptible to an introduced root-rot fungus. In 2020 fewer than 200 plants remained, in poor condition.
Andrew Crawford, Author provided

Things aren’t improving. Scientists recently compiled long-term monitoring of more than 100 threatened plant species at 600 sites nationally. And they found populations had declined on average by 72% between 1995 and 2017.

This is a very steep rate of decline, much greater than for threatened mammal or bird populations.

On the brink

Many species listed as threatened aren’t receiving targeted conservation action or even baseline monitoring, so an important first step in preventing extinctions was identifying the species at greatest risk.

To find the top 50, we looked at the evidence: all available published and unpublished information and expert surveys of over 120 botanists and land managers.
They’re targeted by our Action Plan for Australia’s Imperilled Plants.

Action Plan for Australia’s Imperilled Plants.

Thirty of the species in the plan have fewer than 50 mature individual plants remaining.

And 33 are known only from a single location, such as the Grampians pincushion-lily (Borya mirabilis), which occurs on one rocky outcrop in Victoria. This means the entire population could be destroyed by a single event, such as a major bushfire.

A dead-looking gum tree on agricultural land — About 2,000 Morrisby’s gums were growing in the early 1990s, but by 2016 fewer than 50 remained. Climate change and damage from insects and animals threaten those left. Protecting trees with fencing has led to new seedlings.
Magali Wright, Author provided

Fewer than 10 lax leek-orchids (*Prasophyllum laxum*) remain. Declines are ongoing due to drought and wildfire, and the South Australian species only occurs on private property not managed for conservation. Proposed recovery actions include habitat protection and establishing the orchid and its mycorrhizal fungi in conservation reserves.
Shane Graves, Author provided

Fewer than 15 woods well spyridium (*Spyridium fontis-woodii*) shrubs remain on a single roadside in South Australia. Research into threats and germination requirements is urgently needed, plus translocation to conservation reserves.
Daniel Duval/South Australian Seed Conservation Centre, Author provided

So how can we protect them?

Some of the common management actions we’ve proposed include:

preventing further loss of species’ habitat. This is the most important action required at a national scale
regularly monitoring populations to better understand how species respond to threats and management actions
safely trialling appropriate fire management regimes, such as burning in areas where fires have been suppressed
investing in disease research and management, to combat the threat of phytophthora (root-rot fungus) and myrtle rust, which damages leaves
propagating and moving species to establish plants at new sites, to boost the size of wild populations, or to increase genetic diversity
protecting plants from grazing and browsing animals, such as feral goats and rabbits, and sometimes from native animals such as kangaroos.

Once common, the dwarf spider-orchid (*Caladenia pumila*) wasn’t seen for over 80 years until two individual plants were found. Despite intensive management, no natural recruitment has occurred. Propagation attempts have successfully produced 100 seedlings and 11 mature plants from seed. This photo shows botanist Marc Freestone hand-pollinating dwarf spider-orchids.
Marc Freestone, Author provided

Only 21 mature plants of Gillingarra grevillea (*Grevillea sp. Gillingarra*) remain on a disturbed, weedy rail reserve in southwestern WA. Half the population was destroyed in 2011 due to railway maintenance and flooding. Habitat protection and restoration, and translocations to conservation reserves are needed to ensure its survival.
Andrew Crawford, Author provided

Another common issue is lack of recruitment, meaning there’s no young plants coming up to replace the old ones when they die. Sometimes this is because the processes that triggered these plants to flower, release seed or germinate are no longer occurring. This can include things like fire of a particular intensity or the right season.

Unfortunately, for some plants we don’t yet know what triggers are required, and further research is essential to establish this.

Now we need the political will

Our plan is for anyone involved in threatened flora management, including federal, state, territory and local government groups, First Nations, environment and community conservation groups, and anyone with one of these plants on their land.

The Border Ranges lined fern (*Antrophyum austroqueenslandicum*) and its habitat are exceedingly rare. It’s threatened by drought and climate change, and fewer than 50 plants remain in NSW. If the threat of illegal collection can be controlled, the species would benefit from re-introduction to Queensland’s Lamington National Park.
Lui Weber, Author provided

Plants make Australian landscapes unique — over 90% of our plant species are found nowhere else in the world. They’re also the backbone of our ecosystems, creating the rich and varied habitats for our iconic fauna to live in. Plants underpin and enrich our lives every day.

Now we have an effective plan to conserve the Australian plants at the greatest risk of extinction. What’s needed is the political will and resourcing to act in time.

Jennifer Silcock, Post-doctoral research fellow, The University of Queensland; Jaana Dielenberg, University Fellow, Charles Darwin University; Roderick John Fensham, Associate Professor of Biological Sciences, The University of Queensland, and Teghan Collingwood, Research Technician, The University of Queensland

This article is republished from The Conversation under a Creative Commons license. Read the original article.

5 remarkable stories of flora and fauna in the aftermath of Australia’s horror bushfire season

hamiltonphillipa/iNaturalist, CC BY-NC-SA

Will Cornwell, UNSW; Casey Kirchhoff, UNSW, and Mark Ooi, UNSW

Around one year ago, Australia’s Black Summer bushfire season ended, leaving more than 8 million hectares across south-east Australia a mix of charcoal, ash and smoke. An estimated three billion animals were killed or displaced, not including invertebrates.

The impact of the fires on biodiversity was too vast for professional scientists alone to collect data. So in the face of this massive challenge, we set up a community (citizen) science project through the iNaturalist website to help paint a more complete picture of which species are bouncing back — and which are not.

Almost 400 community scientists living near or travelling across the firegrounds have recorded their observations of flora and fauna in the aftermath, from finding fresh wombat droppings in blackened forests, to hearing the croaks of healthy tree frogs in a dam choked with debris and ash.

Each observation is a story of survival against the odds, or of tragedy. Here are five we consider particularly remarkable.

Greater gliders after Australia’s largest ever fire

The Gospers Mountain fire in New South Wales was the biggest forest fire in Australian history, razing an area seven times the size of Singapore. This meant there nothing in history scientists could draw from to predict the animals’ response.

So it came as a huge surprise when a community scientist observed greater gliders deep within the heart of the Gospers Mountain firegrounds in Wollemi National Park, far from unburned habitat. Greater gliders are listed as “vulnerable” under national environment law. They’re nocturnal and live in hollow-bearing trees.

A greater glider with shining eyes at night — A citizen scientist snapped this photo of a greater glider in the heart of the the Gospers Mountain firegrounds.
Mike Letnic/iNaturalist, CC BY-NC

How gliders survived the fire is still unknown. Could they have hidden in deep hollows of trees where the temperature is relatively cooler while the fire front passed? And what would they have eaten afterwards? Greater gliders usually feed on young leaves and flowers, but these foods are very rare in the post-fire environment.

Finding these gliders shows how there’s still so much to learn about the resilience of species in the face of even the most devastating fires, especially as bushfires are forecast to become more frequent.

Rare pink flowers burnishing the firegrounds

The giant scale of the 2019-20 fires means post-fire flowering is on display in grand and gorgeous fashion. This is a feature of many native plant species which need fire to stimulate growth.

Excitingly, community scientists recorded a long-dormant species, the pink flannel flower (Actinotus forsythii), that’s now turning vast areas of the Blue Mountains pink.

Pink flannel flowers are bushfire ephemerals, which means their seeds only germinate after fire.
Margaret Sky/iNaturalist, CC BY-NC

Pink flannel flowers are not considered threatened, but they are very rarely seen.

Individuals of this species spend most of their life as a seed in the soil. Seeds require a chemical found in bushfire smoke, and the right seasonal temperatures, to germinate.

Rediscovering the midge orchid

Much of Australia’s amazing biodiversity is extremely local. Some species, particularly plants, exist only in a single valley or ridge. The Black Summer fires destroyed the entire range of 100 Australian plant species, incinerating the above-ground parts of every individual. How well a species regenerates after fire determines whether it recovers, or is rendered extinct.

The midge orchid.
Nick Lambert/iNaturalist, CC BY-NC

One of these is a species of midge orchid, which grows in a small area of Gibraltar Range National Park, NSW.

All of the midge orchid’s known sites are thought to have burned in late 2019. The species fate was unknown until two separate community scientists photographed it at five sites in January 2021, showing its recovery.

Like many of Australia’s terrestrial orchids, this species has an underground tuber (storage organ) which may have helped part of it avoid the flames’ lethal heat.

Don’t forget about insects

Despite their incredible diversity and tremendous value to society, insects tend to be the forgotten victims of bushfires and other environmental disasters.

Many trillions of invertebrates would have been killed in the fires of last summer. A common sight during and after the bushfire season was a deposit of dead insects washed ashore. Some died from the flames and heat, while others died having drowned trying to escape.

Dead insects washed up on the beach was a common sight in the fire aftermath.
BlueBowerStudio/iNaturalist, CC BY-NC

One dead insect deposit — one of hundreds that washed up near Bermagui, NSW on Christmas Eve — included a range of species that have critical interactions with other organisms.

This includes orchid dupe wasps (Lissopimpla excelsa), the only known pollinator of the orchid genus Cryptostylis. Transverse ladybirds (Coccinella transversalis), an important predator of agricultural pests such as aphids, also washed up. As did metallic shield bugs (Scutiphora pedicellata), spectacular iridescent jewel bugs that come in green and blue hues.

Some insects died from the flames and heat, while others died having drowned trying to escape the flames.
BlueBowerStudio/iNaturalist, CC BY-NC

The unlikely survival of the Kaputar slug

Creatures such as kangaroos or birds have a chance to flee bushfires, but smaller, less mobile species such as native slugs and snails have a much tougher time of surviving.

The 2019-2020 bushfire season significantly threatened the brilliantly coloured Mount Kaputar pink slug, found only on the slopes of Mount Kaputar, NSW. When fires ripped through the national park in October and November 2019, conservationists feared the slug may have been entirely wiped out.

But park ranger surveys in January 2020 found at least 60 individuals managed to survive, likely by sheltering in damp rock crevices. Community scientists have spotted more individuals since then, such as the one pictured here found in September 2020.

But the slug isn’t out of the woods yet, and more monitoring is required to ensure the population is not declining.

Bright pink slug — A community scientist spotted this rare slug in firegrounds.
Taylor/iNaturalist, CC BY-NC

Continuing this work

While community scientists have been documenting amazing stories of recovery all across Australia, there are still many species which haven’t been observed since the fires. Many more have been observed only at a single site.

The Snowy River westringia (Westringia cremnophila), for instance, is a rare flowering shrub found on cliffs in Snowy River National Park, Victoria. No one has reported observing it since the fire.

So far these community scientist observations have contributed to one scientific paper, and three more documenting the ability for species to recover post-fire are in process.

Recovery from Black Summer is likely to take decades, and preparing a body of scientific data on post-fire recovery is vital to inform conservation efforts after this and future fires. We need more observations to continue this important work.

Will Cornwell, Associate Professor in Ecology and Evolution, UNSW; Casey Kirchhoff, PhD Candidate, UNSW, and Mark Ooi, Senior Research Fellow, UNSW

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Undocumented plant extinctions are a big problem in Australia – here’s why they go unnoticed

Matchstick banksia (*Banksia cuneate*). There are only about 500 of these plants left in the wild at 11 different sites, with much of its habitat having been historically cleared for agriculture.
Andrew Crawford/Threatened Species Hub

David Coates, University of Western Australia

A recent survey on the world’s plants found a shocking number have gone extinct – 571 since 1750. And this is likely to be a stark underestimate. Not all plants have been discovered, so it’s likely other plants have gone extinct before researchers know they’re at risk, or even know they exist.

In Australia, the situation is just as dire. The Threatened Species Recovery Hub recently conducted two evaluations that aren’t yet published of extinct plants in Australia. They found 38 have been lost over the last 170 years, such as the Daintree River banana (Musa fitzalanii) and the fringed spider-orchid (Caladenia thysanochila).

But uncertainty about the number of plant extinctions, in addition to the 38 confirmed, is an ongoing concern.

Both studies pointed out the actual number of extinctions is likely to be far more than those recognised in formal lists produced by the Commonwealth and state and territory agencies.

For example, there is still a high rate of discovery of new plant species in Australia. More than 1,600 plants were discovered between 2009 and 2015, and an estimated 10% are still yet to be discovered.

The extinction of Australian plants is considered most likely to have occurred in areas where there has been major loss and degradation of native bushland. This includes significant areas in southern Australia that have been cleared for agriculture and intensive urbanisation around major cities.

Many of these extinct plants would have had very restricted geographic ranges. And botanical collections were limited across many parts of Australia before broad scale land clearing and habitat change.

Why extinction goes undocumented

There is already one well recognised Australian plant extinction, a shrub in Phillip Island (Streblorrhiza speciosa), which was never formally recognised on any Australian threatened species list.

Black magic grevillea (*Grevilla calliantha*) is known from only six populations within a range of 8 square kilometres. In the wild the species is threatened by frequent fire, habitat loss, invasive weeds, herbicide overspray, grazing animals and phytophthora dieback.
Dave Coates

Researchers also note there are Australian plants that are not listed as extinct, but have not been collected for 50 years or more.

While undocumented extinction is an increasing concern, the recent re-assessment of current lists of extinct plants has provided a more positive outcome.

The re-assessment found a number of plants previously considered to be extinct are not actually extinct. This includes plants that have been re-discovered since 1980, and where there has been confusion over plant names. Diel’s wattle (Acacia prismifolia), for instance, was recently rediscovered in Western Australia.

A significant challenge for accurately assessing plant extinction relates to the difficulties in surveying and detecting them in the Australian landscapes.

Many have histories associated with fire or some other disturbance. For example, a number of plants spend a significant part of their time as long-lived seeds – sometimes for decades – in the soil with nothing visible above ground, and with plants only appearing for a few years after a fire.

But by far, the greatest reason for the lack of information is the shortage of field surveys of the rare plants, and the availability of botanists and qualified biologists to survey suitable habitat and accurately identify the plants.

Purple-wood wattle (*Acacia carneorum*) is slow growing and rarely produces viable seed. Threats are not well understood but grazing by livestock and rabbits is likely to impact on the species.
Andrew Denham

What we’ve learnt

The continuing decline of Australia’s threatened plants suggests more extinctions are likely. But there have been important achievements and lessons learnt in dealing with the main causes of loss of native vegetation.

Our understanding of plant extinction processes – such as habitat loss, habitat degradation, invasive weeds, urbanisation, disease and climate change – is improving. But there is still a significant way to go.

One challenge in dealing with the causes of Australian plant extinction is how to manage introduced diseases.

Two plant diseases in particular are of major concern: Phytophthora dieback, a soil-borne water mould pathogen, and Myrtle rust, which is spread naturally by wind and water.

Both diseases are increasingly recognised as threats, not only because of the impact they are already having on diverse native plant communities and many rare species, but also because of the difficulties in effective control.

Two Australian rainforest tree species Rhodomyrtus psidioides and Rhodamnia rubescens were recently listed as threatened under the NSW legislation because of myrtle rust.

Native guava (*Rhodomyrtus psidioides*) A tree species around the margins of rainforest between the NSW and the QLD border. The species is has now been listed as Critically Endangered. Surveys of rainforest areas infected with Myrtle Rust found that 50 to 95% of native guava trees were killed by the disease within a few years.
Zaareo/Wikimedia

While extinction associated with disease is often rapid, some individual plants may survive for decades in highly degraded landscapes, such as long-lived woody shrubs and trees. These plants will ultimately go extinct, and this is often difficult to communicate to the public.

While individual species will continue to persist for many years in highly disturbed and fragmented landscapes, there is little or no reproduction. And with their populations restricted to extremely small patches of bush, they’re vulnerable to ongoing degradation.

In many such cases there is an “extinction debt”, where it may take decades for extinction to occur, depending on the longevity of the plants involved.

But it’s not all doom and gloom. A recent study found of the 418 threatened Australian plants showing ongoing decline, 83% were assessed as having medium to high potential for bouncing back.

And with long-term investment and research there are good prospects of saving the majority of these plants.

David Coates, Adjunct Professor and Research Associate, University of Western Australia

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The 39 endangered species in Melbourne, Sydney, Adelaide and other Australian cities

File 20190402 177190 cksuwv.jpg?ixlib=rb 1.1 — Threatened species live in cities and towns around Australia, including the critically endangered western swamp tortoise.
Elia Purtle, AAP Image/Perth Zoo

Kylie Soanes, University of Melbourne and Pia Lentini

The phrase “urban jungle” gets thrown around a lot, but we don’t usually think of cities as places where rare or threatened species live.

Our research, published today in Frontiers in Ecology and the Environment, shows some of Australia’s most endangered plants and animals live entirely within cities and towns.

Stuck in the city with you

Australia is home to 39 urban-restricted threatened species, from giant gum trees, to ornate orchids, wonderful wattles, and even a tortoise. Many of these species are critically endangered, right on the brink of extinction. And cities are our last chance to preserve them within their natural range.

Urban environments offer a golden opportunity to preserve species under threat and engage people with nature. But that means we might need to think a little differently about how and where we do conservation, embrace the weird and wonderful spaces that these species call home, and involve urban communities in the process.

Roads to the left of them, houses to the right

When you picture city animals you might think of pigeons, sparrows or rats that like to hang out with humans, or the flying foxes and parrots that are attracted to our flowering gardens.

But that’s not the case here. The threatened species identified in our research didn’t choose the city life, the city life chose them. They’re living where they’ve always lived. As urban areas expand, it just so happens that we now live there too.

The first hurdle that springs to mind when it comes to keeping nature in cities is space: there’s not a lot of it, and it’s quickly disappearing. For example, the magnificent Caley’s Grevillea has lost more than 85% of its habitat in Sydney to urban growth, and many of its remaining haunts are earmarked for future development. Around half of the urban-restricted species on our list are in the same predicament.

It’s especially tough to protect land for conservation in urban environments, where development potential means high competition for valuable land. So when protected land is a luxury that few species can afford, we need to work out other ways to look after species in the city.

Caley’s grevillea has lost 85% of its habitat as Sydney has expanded.
Isaac Mammott

Not living where you’d expect

Precious endangered species aren’t all tucked away in national parks and conservation reserves. These little battlers are more often found hiding in plain sight, amid the urban hustle and bustle.

Our research found them living along railway lines and roadsides, sewerage treatment plants and cemeteries, schools, airports, and even a hospital garden. While these aren’t the typical places you’d expect to find threatened species, they’re fantastic opportunities for conservation.

The spiked rice flower is a great example. Its largest population is on a golf course in New South Wales, where local managers work to enhance its habitat between the greens, and raise awareness among residents and local golfers. These kinds of good partnerships between local landowners and conservation can find “win-win” situations that benefit people and nature.

A series of unfortunate events

It’s no secret that living in the ‘burbs can be risky: a fact best illustrated in the cautionary tale of a roadside population of the endangered Angus’s onion orchid. Construction workers once unwittingly dumped ten tonnes of sand over the patch in the late 1980s, then quickly attempted to fix the problem using a bulldozer and a high-pressure hose. Later, a portaloo was plonked on top of it.

Examples like this show just how important it is for policy makers, land managers and the community to know that these species are there in the first place, and are aware that even scrappy-looking habitats can be important to their survival. Otherwise, species are just one stroke of bad luck away from extinction.

People power

It’s common to think if you want to conserve nature, you need to get as far away from people as you can. After all, we can be a dangerous lot (just ask Angus’s onion orchid). But we also have extraordinary potential to create positive change – and it’s much easier for us to do this if we only have to travel as far as our backyard or a local park.

Many urban-restricted species get support by their local communities. Examples from our research showed communities across Melbourne raising thousands of dollars in conservation crowdfunding, dedicating countless volunteer hours to caring for local habitats, and even setting up neighbourhood watches to combat vandals. This shows a huge opportunity for urban residents to be on the conservation frontline.

Our research focused on 39 species that are restricted to Australian cities and towns today. But that’s not where the opportunity for urban conservation ends.

There are about another 370 threatened species that share their range with urban areas across Australia, as well as countless “common” native species that call cities home. And as cities continue to expand, many other threatened species stand to become urban dwellers. It’s clear that if we only focus conservation efforts in areas far from humans, species like these will be lost forever.

Kylie Soanes, Postdoctoral fellow, University of Melbourne and Pia Lentini, Research Fellow, The University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The humble spade flower moonlights as the ‘love shrub’

File 20190201 112314 r476de.png?ixlib=rb 1.1 — The Conversation

Bronwyn Smithies, The University of Queensland and Edward Kalani Gilding, The University of Queensland

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If you are observant enough in the Australian bush, you may be able to spot the spade flower, a member of the violet family. Spade flowers grow under the semi-shade of open eucalypt forest, among other little green herbaceous plants.

This often-overlooked member of Australian flora hides some interesting secrets, including a rare chemical that may hold the key to turning regular plants into medicinal cures.

The common name spade flower refers to the flower’s shape, which is dominated by the spade-shaped labellum. Its botanical name, Hybanthus enneaspermus, is equally descriptive. The generic name Hybanthus means “humpbacked flower”, referring to the posture of the flowers. Meanwhile, the specific name enneaspermus means “nine-seeded”, because upon maturity each tiny 5mm fruit splits into three sections bearing three seeds each.

A hidden talent

Violets are familiar objects, from the showy native Viola banksii or the scent of European sweet violets. What is not common knowledge is that members of the Violaceae family produce some very curious molecules called peptides.

People – and many other organisms – use peptides as signals that enable communication between cells and tissues. An example of a peptide messenger from humans with an important function is oxytocin, also known as the “love hormone”. Oxytocin regulates social bonding and other key aspects of our biology and sociality. In contrast, plants sometimes use peptides for a different purpose, as toxins to protect themselves from insects and other pests.

But unlike most peptides, those produced by Violaceae are circular instead of linear. Because of this circular shape, they are highly stable in conditions that would degrade other peptides. This special class of peptides are called “cyclotides” and are only found in relatively few plant species. This is why we have been searching all across northern Australia, from the Kimberley region in Western Australia to the Queensland coast, for samples of native Australian Violaceae.

The first cyclotide to grab the attention of scientists comes from an African plant called kalata-kalata, traditionally used in teas to hasten childbirth. In 2013, it was shown that a specific cyclotide from kalata-kalata acts on smooth muscle to cause contraction of muscle tissue.

Kalata-kalata, or *Oldenlandia affinis*, is used in a traditional medicinal tea. It’s efficacy comes from the cyclotides it produces.
KalataB1/Wikipedia

But easing childbirth might not be the only effect cyclotides have. Initial experiments with spade flower extracts demonstrate a significant effect on the mating behaviour of rats. Rats treated with peptide-laden extracts from spade flower exhibit, uh, increased copulation frequency.

In us humans, the receptors that detect peptides control libido, sleep, and other aspects of our biology. These observations leave spade flower cyclotides as prime suspects underpinning this amorous bioactivity, and could be the basis for coining yet another name for this plant: the “love shrub”.

Despite this intriguing effect, until further scientific investigation validates these initial aphrodisiac findings and their basis, it is probably wise to steer clear of ingesting these plants.

Spade flower is indigenous to Australia, but the native range extends through southern Asia, India, and into Africa. Despite the wide range of the species, the plant is usually distributed in a here-and-there fashion. In our experience this sparse distribution has meant finding no sign of them along the roughly 600km Gibb River Road at the end of the wet season, and just a single observation from a roadside south of Gladstone. This scarcity tests the resolve of many skillful plant spotters, ourselves included.

Spade flower buds are delicate and graceful.
Author provided

You’re most likely to find spade flowers in semi-shaded environments north of the Queensland-New South Wales border, along the east coast, and across the Top End. It grows along roadsides or near waterways, but it is difficult to spot because its narrow leaves tend to blend into the mix of herbs growing alongside it.

Look for the lilac spade-shaped flowers among the understory herbs during the warmer and wetter months, but do this before midday when the flowers wilt away from view.

There are other Hybanthus species in Australia, however the genus appears to be polyphyletic (meaning they are grouped together but don’t share a single common ancestor) so the genus is not truly representative of a single taxonomic group per se. Other Hybanthus species look similar to spade flower, namely H. monopetalus, which grows multiple purple-blue flowers on a single stem instead of single lilac-coloured flowers.

In habitats between Brisbane and Sydney spade flower is scarce, however a similar and arguably showier species called H. stellarioides occurs. H. stellarioides is somewhat more delicate, but what really sets it apart are the bright royal orange flowers it produces in summer and autumn.

Spade flowers next to their flashier orange cousin, *H. stellarioides*.
Author provided

In many other aspects these two species look so similar that for some time H. stellarioides was considered a subspecies of the spade flower, however it is now clear they are genetically distinct.

As part of Professor David Craik’s research group at The University of Queensland, we have sequenced the expressed genes of spade flower shoots and roots to uncover how these clever plants make cyclotides. These data helped explain spade flower’s cyclotide amino acid sequences.

Armed with this information, the scientific community can now make stable designer peptides as potential pharmaceuticals. The Craik group is working on making modified cyclotides that can treat cancer and other diseases, and then reintroducing those genes into edible plants – turning a regular tomato plant into a medicinal plant for example. Learning how the spade flower makes cyclotides has already helped us to make some new cyclotides in other plant seeds.

Finally, this work facilitates the isolation of individual “love shrub” cyclotides to test their effects. Watch this space and the herbs underfoot. The humble and shy spade flower may have more surprises yet!

Sign up to Beating Around the Bush, a series that profiles native plants: part gardening column, part dispatches from country, entirely Australian.

Bronwyn Smithies, PhD Candidate, The University of Queensland and Edward Kalani Gilding, Postdoctoral Research Officer, The University of Queensland

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Native cherries are a bit mysterious, and possibly inside-out

File 20181214 178555 acj9vb.png?ixlib=rb 1.1 — John Tann/Flickr, CC BY-SA

Gregg Müller, La Trobe University

People don’t like parasites. But there’s a local Aussie tree that’s only a little bit parasitic: the native cherry, or cherry ballart.

It’s what we call hemiparasitic. It can photosynthesise, but gains extra nutrients by attaching its roots to host plants.

The native cherry, Exocarpos cupressiformis, might be our most widespread root hemiparasite tree, but we’re not quite sure – root-parasitic shrubs and trees are a bit of a research blank spot. We are not even really sure who all the hosts of cherry ballart are.

Although other parasites – like mistletoes – have a more direct Christmas association, cherry ballart does have an Australian Yuletide connection: their conifer-like appearance (the species name cupressiformis means “cypress-like”) was noted by homesick European settlers, who chopped them down for Christmas trees.

On the map

Cherry ballart grows from the Atherton Tablelands in Queensland to southern Tasmania, and across to the Eyre Peninsula in South Australia.

The first European to record it was Jacques-Julien Houtou de Labillardière, the botanist on d’Entrecasteaux’s expedition in search of La Perouse. He formally described the species in 1800, but we have no physical type specimen – the botanical type is his illustration and description. Maybe he lost his specimen, or disposed of it, or thought a picture would do; Jacques seems to have been a bit cavalier with his record-keeping.

Or perhaps it was stolen or misplaced after all his specimens were seized in an overlapping series of defections, wars, defeats and revolution as the expedition tried to return to Europe. The collection was eventually returned after the intercession of English botanist Joseph Banks – but no cherry ballart.

Jacques-Julien Houtou de Labillardière’s description of the native cherry.
Voyage in search of La Pérouse

Its distinctive shape led to native cherry being marked on early Australian orienteering maps, since they are in a cartographic Goldilocks zone: obvious, just numerous enough to make them useful, but not so many as to clutter the map.

That was until Australia held the World Orienteering Championships in the mid-1980s, when the standardisation of Australian orienteering maps for overseas competitors led to the cherry ballart becoming an early victim of internationalisation – at least cartographically speaking.

Its utility also extended to the timber. Among the uses of its “close-grained and handsome wood” are tool handles, gun stocks and map rollers (although the last is probably a niche market these days).

Indigenous Australians ate the fruit, used the wood for spear throwers and reportedly used the sap as a treatment for snakebite. They called it Tchimmi-dillen (Queensland), Palatt or Ballot (Lake Condah, Victoria) and Ballee (Yarra).

Grow baby, grow!

Despite producing large quantities of fruit and seed, no one seems to be able to get native cherry to germinate reliably. There are anecdotal reports that feeding the seed to chooks works, but other growers dismiss this approach.

The edible fruit isn’t actually a true fruit: it’s a swollen stem. It’s reported to have the highest sugar level of any native fruit in the forests of southern Victoria and is much tastier than you’d think a stem would be. (It’s also probably an important nutrient supply for some birds, but that’s yet another thing we are yet to prove.)

This odd “fruit” gives rise to the genus name (exo = outside, carpos = fruit,) and was often touted by early European writers as another example of the topsy-turvy nature of Australia – “cherries” with the pit on the outside went along with “duck-billed playtpus”, animals with pouches, trees that shed bark rather than leaves, and Christmas in the middle of summer.

The sweet and delicious fruit of native cherries is actually a swollen stem.
Arthur Chapman/Flickr, CC BY-NC

Despite their oddness, native cherries in the bush are biodiversity hotspots. My camera trap data show they preferentially attract echidnas, possums, foxes, swamp wallabies, white-winged choughs and bronzewing pigeons.

This might be because they modify their immediate environment. My research shows they create moderate micro-climates in their foliage, reduce soil temperatures, increase soil water retention, concentrate nutrients in the soil beneath their canopies, and alter the understorey vegetation. They also kill some of their host trees, creating patches with higher concentrations of dead timber. All these probably have something to do with their animal attraction, but exactly how is a mystery yet to be solved.

In addition to their attractiveness to vertebrates, native cherries are required hosts for some striking moths and share specialist host duties with mistletoe for some of our most beautiful butterflies (although mistletoes take most of the glory in the scientific literature).

My research into our cherry ballart hopes in part to correct these historical slights. I want to set the record straight on this overlooked widespread and attractive little tree, which has a long indigenous use and was one of the first of our native flora to be described by Europeans.

Sign up to Beating Around the Bush, a series that profiles native plants: part gardening column, part dispatches from country, entirely Australian.

Gregg Müller, Lecturer in Natural History, La Trobe University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Warty hammer orchids are sexual deceivers

File 20181129 170226 u1w9ow.png?ixlib=rb 1.1 — The Conversation, CC BY-SA

Ryan Phillips, La Trobe University

Orchids are famed for their beautiful and alluring flowers – and the great lengths to which people will go to experience them in the wild. Among Australian orchids, evocative names such as The Butterfly Orchid, The Queen of Sheeba, and Cleopatra’s Needles conjure up images of rare and beautiful flowers.

Yet there is a rich diversity of our orchids. Some are diminutive, warty, and unpleasant-smelling, bearing little resemblance to a typical flower.

While many orchid enthusiasts have a soft spot for these quirky members of the Australian flora, what has brought them international recognition is their flair for using some of the most bizarre reproductive strategies on Earth.

The Conversation/Ryan Phillips/Suzi Bond., CC BY

Sexual mimicry

From the very beginnings of pollination research in Australia there were signs that something unusual was going on in the Australian orchid flora.

In the 1920s Edith Coleman from Victoria made the sensational discovery that the Australian tongue and bonnet orchids (Cryptostylis) were pollinated by males of a particular species of ichneumonid wasp attempting to mate with the flower.

But this was just the beginning.

The King-in-his-carriage, Drakaea glyptodon, is the most common species of hammer orchid. Here the flower is pictured next to the female of its pollinating thynnine wasp, Zaspilothynnus trilobatus.
Rod Peakall, Author provided

We now know that while the insect species involved may vary, many of our orchid species use this strategy. Australia is the world centre for sexual deception in plants.

Perhaps the most sophisticated flower of all sexually deceptive plants is seen in the hammer orchids, a diminutive genus that only grows in southwestern Australia. Their solitary stem reaches a height of around 40cm, and each stem produces a single flower no more than 4cm in length.

Even among sexually deceptive orchids, hammer orchids stand out from the crowd. They have a single heart-shaped leaf that sits flush with the soil surface, and grow in areas of dry inhospitable sand – an unusual choice for an orchid.

The thynnine wasp Zaspilothynnus nigripes is a sexually deceived.
pollinator of the Warty hammer orchid. Here they are pictured in copula, with the
flightless female having been carried to a food source by the male.
Keith Smith, Author provided

And then there is the flower. Not only does the lip of the flower more closely resemble an insect than a petal, but it is hinged partway along. All of which starts to makes sense once you see the pollinators in action.

Like many other Australian sexually deceptive orchids, they are pollinated by thynnine wasps – a unique group in which the male picks up the flightless female and they mate in flight.

In the case of hammer orchids, the male grasps the insect-like lip and attempts to fly off with “her”. The combination of his momentum and the hinge mechanism swings him upside down and onto the orchid’s reproductive structures.

It’s not me, it’s you (you’re a flower)

So, how do you trick a wasp?

Accurate visual mimicry of the female insect does not appear to be essential, as there are some sexually deceptive orchids that are brightly coloured like a regular flower.

Instead, the key ingredient for attracting pollinators to the flower is mimicking the sex pheromone of the female insect. And boy, is this pheromone potent.

Indeed, one of the strangest fieldwork experiences I’ve had was wasps flying through my open car window while stopped at traffic lights, irresistibly drawn to make love to the hammer orchids sitting on the passenger seat!

Pollination of the Warty hammer orchid by a male of the thynnine wasp Zaspilothynnus nigripes.
Suzi Bond, Author provided

While determining the chemicals responsible for attraction of sexually deceived pollinators is a laborious process, we now know that multiple classes of chemicals are involved, several of which were new to science or had no previously known function in plants.

What’s more, we are still discovering new and unexpected cases of sexual deception in orchids that don’t conform to the insect-like appearance of many sexually deceptive orchids.

A classic example is the case of the Warty hammer orchid and the Kings spider orchid – these two species have totally different-looking flowers, yet both are pollinated by the same wasp species through sexual deception.

While the ability to attract sexually excited males without closely resembling a female insect may partly explain the evolution of sexual deception, it does not explain the benefit of evolving this strategy in the first place.

A leading hypothesis for the evolution of sexual deception is that mate-seeking males be more efficient at finding orchid flowers than food-foraging pollinators – but this remains a work in progress.

The life cycle of the Warty hammer orchid and its pollinator species,
highlighting the complex ecological requirements needed to support a population of.
the orchid.
Martin Thompson, Author provided

From a conservation point of view, pollination by sexual deception has some interesting challenges. Female animals produce sex pheromones that only attract males of their own species. This means an orchid that mimics a sex pheromone typically relies on a single pollinator species. As such, conservation of any given orchid species requires the presence of a viable population of a particular pollinator.

Further, an interesting quirk of these sexually deceptive systems is the potential for cryptic forms of the orchid: where populations of orchids that appear identical to human observers actually attract different pollinator species through shifts in pheromone chemistry. Indeed, of the ten known species of hammer orchid, three contain cryptic forms.

Read more:
Australia’s unusual species

Not only does this create a major challenge for managing rare species, it raises the possibility that – should these forms prove to be separate species – the true diversity of sexually deceptive orchids could be greatly underestimated.

Sign up to Beating Around the Bush, a series that profiles native plants: part gardening column, part dispatches from country, entirely Australian.

Ryan Phillips, Senior Lecturer in Ecology, Environment & Evolution, La Trobe University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The Lord Howe screw pine is a self-watering island giant

File 20180824 149475 1045iq3.png?ixlib=rb 1.1 — To grow tall enough to reach the canopy, a species of screw pine unique to Lord Howe Island has evolved its own rainwater harvesting system.
Matthew Biddick, CC BY-SA

Matthew Biddick, Victoria University of Wellington

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Pandanus forsteri, a species of screw pine endemic to Lord Howe Island, grows tall like no other tree on Earth. To reach the canopy, these trees have evolved a rainwater harvesting system that enables them to water themselves.

Originally from Micronesia, the palm-like P. forsteri belongs to a group of trees that have populated almost every coastal habitat of the Pacific. In fact, pandans are used by Oceanic cultures for everything from fishing and cooking to medicine and religious ceremonies.

Our research shows that pandans differ in several fundamental ways from more familiar trees, including how they capture water and grow.

Reaching for the canopy

Most trees lay down concentric rings of vascular tissue as they mature, thickening over time. This enables them to grow tall, yet maintain enough structural integrity to avoid toppling over. It is also arguably the most important evolutionary innovation that has enabled trees to colonise most of terrestrial Earth.

Together with palms, bamboo and yucca, pandans belong to a group known as monocots, because their seedlings produce a single embryonic leaf.

Pandans belong to a group of plants whose vascular tissue is still primitive, making it difficult to grow tall.
Ian Hutton, CC BY-SA

Their vascular tissue is not compartmentalised in the same way. It forms bundles that are positioned somewhat haphazardly within the stem. Consequently, monocots are unable to produce true secondary growth and thicken like other trees do – and reaching the canopy becomes a much more ambitious endeavour.

The canopy offers a good life. The sun is shining, seed-dispersing birds are abundant, and the herbivores of the forest floor are a distant concern. In monocots, natural selection has favoured some inventive ways of stretching to the top.

Pay-as-you-go growth

Palms overcome the limitations imposed by their physiology by spending their younger years laying down enough vascular girth to support their future stature. Think of it like putting aside money for your retirement. You may not need it now, but you will likely later depend on it.

Stilt roots support the crown as it matures.
Kevin Burns, CC BY-SA

Once thick enough, palms shift their efforts to vertical growth. The palm’s tactic of delayed vertical growth may be slow, but it functions well enough to thrust Columbian wax palms (Ceroxylon quindiuense) – the world’s tallest monocot – 45 meters into the clouds.

Pandans, on the other hand, are less patient. Unlike palms, they prefer a sort of “pay-as-you-go” method. They produce stilt roots that extend from the trunk to the ground for support as the crown matures. The end result gives the appearance of an ice cream cone perched on a tepee of stilts. It’s an odd strategy, but it works.

However, on Lord Howe Island, something quite remarkable has transpired. Isolated some 600 kilometres off the east coast of Australia, one species of screw pine has evolved into an island giant.

Lord Howe Island, some 600km off the Australian east coast, is home to countless endemic plants and animals.
Ian Hutton, CC BY-SA

Island syndrome

Most screw pines are lucky to reach four or five meters. Pandanus forsteri trees, however, regularly exceed 15 meters. These kinds of size changes are not uncommon on isolated islands. They are part of a repeated evolutionary phenomenon known as the island syndrome.

Species on isolated islands are free from the stressors of continental life, and they subsequently converge on a more optimal, ancestral form. Large continental species evolve into island dwarfs, while smaller species become comparatively gigantic. Support for the island syndrome primarily comes from animals. However, a growing body of evidence suggests island plants follow a similar evolutionary path.

A network of aqueducts on the root surface guides water to the absorptive tissue at the tip of the growing root.
Matt Biddick, CC BY-SA

While gigantism may be favourable, it doesn’t come without risks – and for P. forsteri, they are serious. Thanks to their new-found stature, P. forsteri trees must produce enormous stilt roots to support themselves. This process that can take years. Exposed to the air, roots can form air bubbles, and an air bubble in a plant is bad in the same way it is bad in your artery. It is potentially lethal.

Nature appears to have solved this problem through the evolution of a rainwater harvesting system that enables P. forsteri to water its own stilt roots before they reach the ground.

Gutter-like leaves collect rainwater and transport it to the trunk, where it descends. The flow of water is then couriered by a network of aqueducts formed by the root surface. Finally, water is stored in a specialised organ of absorptive tissue encasing the growing root tip.

Back to the drawing board

This is dramatically different from how we traditionally think about plants. It is far from our concept of sessile beings that passively absorb everything they need from the soil, thanks to the capillary action of their vascular tissues. Never before has a plant species been shown to possess a system of traits that operate jointly to capture, transport and store water external to itself.

This species has opened our eyes to an entirely new field of scientific inquiry. It forces scientists to rethink the function of organs like leaves and roots outside of the contexts of photosynthesis and the conduction of soil water.

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Do other plants harvest rainwater in this way? Why have we only just discovered this? Has our overly simplistic view of plants hindered our ability to comprehend their true complexity? Only time, and more research, will tell.

Matthew Biddick, PhD Researcher, Victoria University of Wellington

This article was originally published on The Conversation. Read the original article.

What happens when fires become more frequent?

What happens when fire seasons get longer?

When drought and heatwaves get more severe

When threats pile up

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Sydney golden wattle (Acacia longifolia subspecies longifolia)

Coast wattle (Acacia longifolia subspecies sophorae)

Coast teatree (Leptospermum laevigatum)

A call to action

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What’s driving the loss?

On the brink

So how can we protect them?

Now we need the political will

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Greater gliders after Australia’s largest ever fire

Rare pink flowers burnishing the firegrounds

Rediscovering the midge orchid

Don’t forget about insects

The unlikely survival of the Kaputar slug

Continuing this work

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Why extinction goes undocumented

What we’ve learnt

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Stuck in the city with you

Roads to the left of them, houses to the right

Not living where you’d expect

A series of unfortunate events

People power

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A hidden talent

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On the map

Grow baby, grow!

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Sexual mimicry

It’s not me, it’s you (you’re a flower)

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Reaching for the canopy

Pay-as-you-go growth

Island syndrome

Back to the drawing board

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