‘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.

Orchids like this may be what comes to mind when you think of them, but there are actually more 30,000 different orchid species.
Shutterstock

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 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: (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.

Swamp wallabies and long-nosed bandicoots may disperse the underground orchid seeds, but they’re locally extinct in WA.
Shutterstock

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.

A leek orchid.
Shutterstock

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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Read more:
Leek orchids are beautiful, endangered and we have no idea how to grow them

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Mark Clements, Botanist, CSIRO

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

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Orchids

Warty hammer orchids are sexual deceivers

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.

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

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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.

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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.

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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.

Orchid: Masters of Lying and Deception

Hunter Region Botanic Gardens

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ABOVE: The Southern Wetlands Boardwalk – Hunter Region Botanic Gardens

Late last week I decided I should do something with the final day of my annual leave that I had taken this time round, so I thought I’d pop into the Hunter Region Botanic Gardens near Raymond Terrace in New South Wales, Australia. I had been here before, but that was a long time ago. I wasn’t impressed on that first visit, so after more then a decade had it improved? Well that was the question I was keen to answer.

ABOVE: The Rotunda  BELOW: Succulents Section

There was a $4.00 ‘escape’ fee, which would allow a token to be purchased and then the boom gate would rise once it was placed into the proper slot at the exit. So no entrance fee, just an exit fee. I was willing to pay this for a quick look and…

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