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).




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‘Plant blindness’ is obscuring the extinction crisis for non-animal species


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.




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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.




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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.




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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.The Conversation

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.

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



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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.


Credit: Elia Purtle

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.




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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.The Conversation

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’



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The Conversation

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

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


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.




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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.



The Conversation

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.




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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.The Conversation

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.




Read more:
Warty hammer orchids are sexual deceivers


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.



The Conversation

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).




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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.




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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.The Conversation

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.




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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.The Conversation

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



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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.




Read more:
Welcome to Beating Around the Bush, wherein we yell about plants


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.




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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.

Figs, ferns and featherwoods: learn all about Australia’s native trees and plants


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You love Australian plants, I love Australian plants, we all love Australian plants!
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Madeleine De Gabriele, The Conversation and Molly Glassey, The Conversation

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Australia is classified as “megadiverse” meaning it’s a global hotspot for plant and animal diversity, and has vast numbers of unique species found nowhere else on Earth. With this newsletter we want you to be able to wander down the garden path, off the beaten track, and smell the gum leaves. Specifically, what kind of gum leaf? What is it from? Where does it grow?




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We’ll let you know every time a new edition in our Beating Around the Bush series comes out, putting the spotlight on a different native plant every time. We’re on a roughly fortnightly schedule, but like any garden there might be a few surprises along the way. I’ll also be rounding up some of the greatest hits from our archives, and talking about what’s new in the plant world.

This one is for all you floraphiles out there.
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The ConversationIf someone else in your life might enjoy this mix in their inbox, please let them know about it. And if you have any feedback, feel free to let us know in the comments.

Madeleine De Gabriele, Deputy Editor: Energy + Environment, The Conversation and Molly Glassey, Audience Development Manager, The Conversation

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