‘Like finding life on Mars’: why the underground orchid is Australia’s strangest, most mysterious flower



Rhizanthella speciosa from Barrington Tops.
Author provided

Mark Clements, CSIRO

If you ask someone to imagine an orchid, chances are pots of moth orchids lined up for sale in a hardware store will spring to mind, with their thick shiny leaves and vibrant petals.

Moth orchids with purple flowers in a pot
Orchids like this may be what comes to mind when you think of them, but there are actually more 30,000 different orchid species.
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But Australia’s orchids are greater in number and stranger in form than many people realise. Rock orchids, fairy orchids, butterfly orchids, leek orchids and even onion orchids all look more or less the same. But would you recognise a clump of grass-like roots clinging to a tree trunk as an orchid?

What about a small, pale tuber that spends its whole life underground, blooms underground and smells like vanilla? This is the underground orchid, Rhizanthella, and it’s perhaps the strangest Australian orchid of them all.

Even to me, having spent a lifetime researching orchids, the idea of a subterranean orchid is like finding life on Mars. I never expected to even see one, let alone have the privilege of working on them.

Known for almost a century, but rarely seen

The family Orchidaceae is the largest group of flowering plants on Earth, comprising more than 30,000 species. Australia is home to around 1,550 species and 95% are endemic, meaning they don’t occur naturally anywhere else in the world.

Rhizanthella has been known to science since 1928, when a farmer in Western Australia who was ploughing mallee for wheat fields noticed a number of tuber-like plants among the roots of broom bushes. Recognising them as unusual, he sent some specimens to the Western Australian Herbarium.

The species Rhizanthella gardneri occurs in Western Australia.
Fred Hort/Flickr, CC BY-SA

In 1931, another underground orchid was discovered in eastern Australia at Bulahdelah in NSW by an orchid hunter who was digging up a hyacinth orchid and found an unusual plant tangled in its roots. Three quarters of a century later, I was involved in conserving the population of Rhizanthella in this location when the Bulahdelah bypass was built.

And most recently, in September, I confirmed an entirely new species of underground orchid, named Rhizanthella speciosa, after science illustrator Maree Elliott first stumbled upon it four years ago in Barrington Tops National Park, NSW.

Elliott’s discovery brings the total number of Rhizanthella species known to science to five, with the other two from eastern Australia and two from Western Australia.

The pink flower head of the _Rhizanthella speciosa_
The newly discovered species, Rhizanthella speciosa, found in Barrington Tops.
Mark Clements, Author provided

All species are vulnerable

For much of its life, an underground orchid exists in the soil as a small white rhizome (thickened underground stem). When it flowers, it remains hidden under leaf litter and soil close to the surface, its petals think and pink, its flower head a little larger than a 50 cent coin.




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Its pollinator is probably a tiny fly that burrows down to lay eggs in the orchid, mistaking the flower for a fungus.

Today, all Rhizanthella species are vulnerable: the species R. gardneri and R. johnstonii are listed as critically endangered under national environment laws, while R. slateri and and R. omissa are listed as endangered. The most recently discovered species hasn’t yet been listed, but its scarcity means it’s probably highly vulnerable.

Rhizanthella speciosa. The seeds of underground orchids are like ball bearings, and the fruits smell like vanilla.
Mark Clements, Author provided

The conservation of the underground orchid is complicated. Knowing where it exists, and where it doesn’t, is one problem. Another is knowing how to grow it.

All orchid species need a buddy, a particular soil fungus, for their seeds to germinate, and Rhizanthella must have its habitat to survive. Unfortunately, it’s extremely difficult to just grow it in a pot.

Seeds like ball bearings

We also know very little about the biology of Rhizanthella. But here’s what we do know.

We’ve discovered the fungus that buddies up with underground orchids in Western Australia is indeed the same as that in eastern Australia. We know underground orchids tend to grow in wetter forests and that burning will kill them. And we know that after pollination, the seed head of an underground orchid takes 11 months to mature.

The floral structures of four described species of _Rhizanthella_
The floral structures of four described species of Rhizanthella: (a) R. slateri (b) R. omissa (c) R. johnstonii (d) R. gardneri
Chris J. Thorogood, Jeremy J. Bougoure et Simon J. Hiscock/Wikimedia, CC BY-SA

Most orchids have wind-dispersed seeds. Some are so light that drifting between Queensland and Papua New Guinea might be possible, and might explain its vast distribution.

The seeds of underground orchids, however, are like ball bearings and the fruits smell like the famous vanilla orchid of Mexico, whose seeds and pods add scent and flavour to everything from candles to ice cream.

In nature, bats disperse the seeds of the vanilla orchid. So we set up infra-red cameras in Bulahdelah as part of the bypass project to find out what animals might disperse the seeds of the underground orchid. We observed swamp wallabies and long-nosed bandicoots visiting the site where R. slateri grows.

We suspect they disperse the seeds of underground orchids via their excrement, finding the orchid among truffles and other goodies in the leaf litter and soil of the forest floor.

A swamp wallaby in the bush
Swamp wallabies and long-nosed bandicoots may disperse the underground orchid seeds, but they’re locally extinct in WA.
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In Western Australia, these animals are locally extinct. Without bandicoots and wallabies to transport seeds away from the parent plant, the natural cycle of renewal and establishment of new plants has been broken. This cannot be good for the long-term survival of the two Western Australian Rhizanthella species.

An alien in the floral world

Conservation of the underground orchid might require intricate strategies, such as reintroducing bandicoots to a protected area, preventing bushfires and using alternatives to burning to manage the land.

An important first step is to find more populations of underground orchids to help us learn more about them.

Leek orchid
A leek orchid.
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Our work with DNA has shown, in the orchid family tree, Rhizanthella is most closely related to leek orchids (Prasophyllum) and onion orchids (Microtis).

But as you can see from the photo of a leek orchid above, it bears no resemblance to a subterranean flower, like an alien in the floral world.




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Mark Clements, Botanist, CSIRO

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

Torpor: a neat survival trick once thought rare in Australian animals is actually widespread



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Chris Wacker, University of New England

Life is hard for small animals in the wild, but they have many solutions to the challenges of their environment. One of the most fascinating of these strategies is torpor. Not, to be confused with sleep or Sunday afternoon lethargy, torpor is a complex response to the costs of living.

To enter torpor, an animal decreases its metabolism, reducing its energy requirements. A torpid animal will often be curled in a tight ball in its nest and look like it’s sleeping.

Once thought to occur only in birds and mammals in the Northern Hemisphere where winters are more pronounced, we now know torpor is widespread in small Australian mammals, and has also been observed in many small Australian bird species.

An echidna in the bush.
Echidnas use torpor to save energy.
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Masters of metabolism

Birds and mammals are endotherms and can maintain a high and constant body temperature independent of the environmental temperature, thanks to their high metabolic rate. This allows them to be active across a wide range of environments.

The downside? This high metabolic rate requires a lot of food to fuel it. By reducing the metabolism in a very controlled manner and entering torpor, an animal can live on less energy.

With a lower metabolic rate, the animal’s body temperature decreases — sometimes by as much as 30°C. How low it goes can depend on the extent of the metabolic reduction and the temperature of animal’s immediate environment. The reduced body temperature further lowers the metabolic rate.

Slowing down to survive

Torpor is an extremely effective survival strategy for small endotherms. For example, small mammals have been observed using torpor after bushfires.

Take the brown antechinus, for example. When other animals have fled, this 30g marsupial hides in refuges, waits out the fire, then uses torpor to cope with reduced food availability until local vegetation and invertebrate populations recover.

A brown antechinus on a tree.
The brown antechinus uses torpor to cope with reduced food availability after bushfire.
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Many pregnant and lactating bats and marsupials, and even the echidna, synchronise torpor with reproduction to cope with the energetic costs of mating, pregnancy or lactation.

There are two main types of torpor: daily torpor and hibernation.

Daily torpor

Animals that use daily torpor can do so for approximately 3-6 hours a day as needed.

Daily torpor is common in, but not exclusive to, endotherms living in arid areas, such as the fat-tailed dunnart. This species is a carnivorous marsupial and has a diet of insects and other invertebrates, which may be in short supply in winter.

A fat-tailed dunnart.
When finding enough food is difficult, the fat-tailed dunnart uses torpor.
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Weighing approximately 12 grams as adults, the fat-tailed dunnart may need to eat its body weight in food each day. When finding enough food is difficult, it uses torpor; foraging in the early part of the night then entering torpor in the early morning. Fat-tailed dunnarts reduce their metabolic rate, and subsequently their body temperature, from 35 °C to approximately 15°C, or the temperature of their underground nest.

Hibernation

Animals that hibernate lower their metabolic rate further and have longer torpor bouts than those that use daily torpor. An example of an Australian hibernator is the eastern pygmy possum, a 40g marsupial found in south eastern Australia that hibernates regularly, decreasing its body temperature from approximately 35 °C to as low as 5°C.

When active, this species can survive for less than half a day on 1g of fat, but when hibernating, it can survive for two weeks.

A torpid eastern pygmy possum. Note the curled posture.
Photo credit: Chris Wacker, Author provided

If it weren’t for the periodic increases in metabolic rate and body temperature, a hibernating pygmy possum could live for well over three months on 1g of fat. However, the exact purpose of these periodic arousals is unknown.

The metabolic rate during pygmy possum hibernation is just 2% of the minimum metabolic rate endotherms at a normal body temperature need to live. This baseline metabolism is called basal metabolic rate.

An American black bear
Black bears can’t hibernate with a lower body temperature.
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Compare this with a well-known hibernator, the American black bear.

At approximately 120kg, its metabolic rate during hibernation decreases to 25% of the basal metabolic rate, and the body temperature decreases from approximately 37°C to 30 °C. Black bears can’t hibernate with a lower body temperature, perhaps because it would take them a very long time to reduce it, and then cost them too much energy to rewarm at the end of hibernation.

Can humans do it?

The question people often ask about torpor, is “can humans do it?” Interestingly, some small primates have been observed using torpor. While it is technically possible to induce torpor in humans chemically, torpor is a very complex physiological process, and there are many aspects of it scientists still don’t fully understand.

A gray mouse lemur in Madagascar.
The grey mouse lemur in Madagascar is among the primates that uses torpor.
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Coping with climate change

Australia’s wildlife have evolved strategies to cope with life in an often-harsh environment affected by multiple year-long droughts, landscape-altering floods, and widespread bushfires.

Climate change is predicted to increase the duration, frequency and severity of these events, and in conjunction with landscape clearing, animals are facing new environmental and resource challenges.

While animals that use flexible, daily torpor may be well-suited to cope during these times, at least in the short term, hibernators that depend on long winters are most at risk.




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The Conversation


Chris Wacker, Postdoctoral Research Fellow – School of Environmental and Rural Science, University of New England

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