Nardoo, the desert fern
The recent Queensland floods will trigger the germination of one of the strangest and most notorious plants in Australia.
As the 60-year-old DC3 aeroplane bumps and buzzes down to the outback Queensland town of Birdsville, I gaze out the window in amazement. Instead of a dry, dusty plain, a vast shining lake spreads out below, etching a sharp outline around the little town and dwarfing it in the middle of a sea of water. Pelicans and seagulls zoom about. But this isn't an ocean, it is the local Diamantina River in flood, a once-every-decade-or-two occurrence.
That was back in April 2000. People thought it was only a moderate flood with a peak of around 7.4m, but it inundated towns and properties, isolating inhabitants for weeks.
While the locals were trying to stay high and dry, one of Australia's most fascinating plants was getting a new lease of life. Driving along the muddy roads to a nearby sheep station, I noticed a pretty plant growing thickly in channels of water on the side of the road. It looked like a field of large four-leaf clover, rusty red in the centre, fading out to brilliant green around the edges. This was my first encounter with the aquatic fern known as Common Nardoo, Marsilea drummondii.
Looking into its biology and history, I discovered many sides to this unpredictable little plant: its importance as a food for Aboriginal people, the challenges it presents for cattle and sheep farmers and most notoriously, the role it played in the fate of Australia's most famous explorers.
A flooded past
If you track the Diamantina River to its source in west Queensland, you'll find a vast catchment, part of the Channel Country, covering 119,000 square kilometres. The river rises in the Swords Range, 70 kilometres south-west of Kynuna and flows north and east, before swinging around to the south-west.
Eventually, it passes through Birdsville and crosses over the border into South Australia, emptying in to the vast basin of Lake Eyre, thousands of kilometres from its source. Along the way, there are many opportunities for the Diamantina to leap its banks and spill out onto the flat plains. Not surprisingly, the river has a track record of flooding, with major floods peaking at over 8 metres occurring in 1950, 1974, 1991, 2004 and 2007.
When: Nardoo plants shoot up whenever significant rains come to the inland – and produces its spores on damp mud as the floodwaters recede. Sixty species of the genus Marsilea occur worldwide, with eight in Australia, and six of these endemic.
Where: Inland in all states of Australia, including Tasmania. Habitats include rivers, billabongs, lakes and flood plains.
Life saver or life taker?
In August 1860, Robert O'Hara Burke led an expedition of men, including William John Wills as surveyor, out of Melbourne. Their aim was to be the first people to cross the continent from south to north.
Burke and Wills planned to open up a route that would connect the newly invented telegraph line to Europe, via Java. They wanted to investigate a possible route for a railway line and discover if there was an inland sea.
Three months after setting out, Burke and Wills set up a base camp in Coopers Creek and were running out of food. They were offered nardoo by the local Aborigines and gladly accepted it. It satisfied their appetite and soon after, they began to prepare their own nardoo, grinding it up and mixing it with water to make a thin paste, as they had seen the local people do.
Despite eating up to "four or five pounds a day between us", as Wills notes in his journal, the two explorers grew weaker and thinner and developed symptoms such as shaking legs and a gradually slowing pulse.
On Wednesday, June 12, 1861 Wills wrote... "King out collecting nardoo. Mr Bourke and I at home, pounding and cleaning. I still feel myself, if anything, weaker in the legs, although the nardoo appears to be more thoroughly digested."
Wills couldn't understand why he seemed to be starving, despite eating so much nardoo. What he didn't know was that nardoo contains an enzyme called thiaminase that breaks down thiamine (Vitamin B1), making it unavailable to the body. Thiamine, although needed in only tiny amounts, is essential for energy metabolism, nerve and brain function. We need thiamine to make ATP, a complex molecule that provides energy for cells to do work. People with low thiamine levels also produce too much cholinesterase, an enzyme that regulates nerve impulses that, when disrupted, can interfere with the peripheral nervous system.
Some other plants also contain thiaminase, such as horsetails and bracken fern, and some types of seafood. Nardoo has 100 times more of this enzyme than bracken.
Typical symptoms of thiamine deficiency — a disease known as Beri-Beri — are tremors of the hands, feet and legs, an enlarged heart and weakness. As your body can't use the food you eat to provide energy to its cells, you slowly starve to death, even if you have enough food.
But there may be worse ways to go. As Wills wrote four days before he died, "Starvation on nardoo is by no means very unpleasant, but for the weakness one feels, and the utter inability to move oneself, for as far as the appetite is concerned, it gives me the greatest satisfaction."
The tragedy of this story is that nardoo could have saved Burke and Wills. They failed to add the extra step in the preparation of nardoo that indigenous people followed. Aboriginal people would roast the spore cases (sporocarps), before grinding them. This simple step of adding heat to the process completely breaks down the thiaminase, making it harmless.
Nardoo was a such an important food source to Aboriginal people that it was processed in large amounts with so-called 'Nardoo Mills' — sets of flat grinding stones scattered around the edges of water courses such as the Willandra Lakes.
Perhaps if Burke and Wills had watched the locals more carefully, they might have survived to become the first white men to cross the continent from south to north.
Today, cattle and sheep on grazing properties in inland Australia will succumb to nardoo if they eat enough of it when the sporocarps are present. Although it is fatal to mammals, nardoo is an important flood-time food for waterfowl.
Worth the wait
The massive 'fields' of nardoo that cover the floodplains during a Big Wet are just one chapter in a somewhat complicated personal life. Being a fern, nardoo has no flowers or seeds, instead producing spores.
The adult plant is called a sporophyte. As the fronds of the sporophyte grow, they give a clue to the origins of the nardoo as a fern. The young leaves coiled within the growing point unfurl, just like those of the more familiar tree ferns and bracken ferns.
When the fern matures, it produces hard, nut-like objects up to nine millimetres long called sporocarps, which grow from the rhizome (underground stem/root). The sporocarp is a hard capsule full of spores in starchy packing.
The sporocarps find their way down to accumulate in the bottom of cracks that form in the drying mud. Here they may remain as long as 30 years. When the sporocarps are flooded the starchy packing swells up to a jelly-like substance, bursting the shell and liberating the spores. The spores germinate in this mass, producing tiny, intermediate plants called a prothallus (plural prothalli). The prothallus can be either male or female, producing sperm or eggs accordingly. When an egg is fertilized by a sperm, it grows into a mature spore-bearing sporophyte, the plant we recognise as nardoo and the cycle begins over again. Interestingly, all other living ferns produce just one type of prothallus, not separate male and female forms. It is this degree of specialisation that makes the nardoo genus, Marsilea, the most advanced of all ferns.
Today, nardoo is cultivated by the horticultural industry, not as a source of food, but as a charming feature for the garden. It makes an excellent plant for aquariums and fish ponds as it will grow for years in water, attracts frogs, tolerates both sun and shade and doesn't compete with other water plants. So next time you're wandering around a plant nursery, introduce yourself to nardoo — and spare a thought for Burke and Wills.
- A Fern which Changed Australian History. Calder Chaffey. Far North Coast Group of the Australian Plants Society newsletter. Oct-Nov 2000.
- Thiaminases. Cornell University Department of Animal Science, Toxic Agents List. 2001.
- Marsilea drummondii. Naomi Brydon. In: Growing Native Plants. Australian National Botanic Gardens, Department of the Environment and Water Resources. 2004
- Marsilea drummondii, Common Nardoo. A Braun. Taxon Attribute Profile. Water for a Healthy Country, CSIRO. 2004
- Nardoo. In: Aboriginal Plant Use, NSW Southern Tablelands. Australian National Botanic Gardens. 2007
- Marsileaceae. In: Electronic Pteridophyte Flora of Australia. Australian National Botanic Gardens. 2007
- Flood Warning System for the Diamantina River. Bureau of Meteorology. 2005.
Published 08 March 2007