The Green Dinosaur

(Idiospermum australiense)

By Steve Wilson

Many people who visit this amazing ancient rainforest never realise how close we came to losing it forever. If it wasn’t for the rediscovery of a very special species of tree this whole area could all be farm land and developed now.

Introducing the Green Dinosaur otherwise known as Idiot Fruit a name it gets from its scientific name of Idiospermum it is also known as Ribbonwood. This ancient, enigmatic tree is a member of the angiosperm family which incudes all other flowering plants on the planet. But what makes it so special is that it was one of the first flowering plants to appear on earth.

It is what we call a “relic” species a survivor from a distant past that has somehow managed to survive until today. They are endemic to the Daintree Rainforest which means they are not found anywhere else in the world. It is a tree that has taught us a lot about flowering plant evolution and that has also raised more questions about the age and importance of the Daintree region.

First located south of Cairns by timber cutters in the late 1800s and brought to the attention of a German botanist named Ludwig Diels in 1902 who recognised it as something of special interest to science. He managed to document it and collected some flowers which he took to the Berlin Herbarium. Unfortunately, the specimens collected by Diels were destroyed in a fire caused by the bombing raids of the allies in 1943, by the time he managed to get to the site to collect more samples it had already been clear felled and was thought to be lost forever. Its only known location was now being used for raising sugar cane crops. For years scientists failed to recognise just how unique this tree is. They said Diels had discovered a mere garden plant that had somehow managed to find its way to the Queensland rainforest.

Luckily in 1971 it was rediscovered over the Daintree River after some cows died from eating its toxic seeds. It was John Nichols a Daintree grazier who first reported to the police that someone was poisoning his cows. Luckily the police called in a government vet who performed autopsies on the affected animals. Doug Claque was that vet and while he was at the site another cow died. He discovered almost intact idiot fruit seeds in the cow’s stomach that had been swallowed whole. He noticed that the cows went into spasms after eating the seeds then the nerves would be paralysed and they would die. An important discovery for the future of the rainforest not so fortunate for the cows. He then sent specimens to the Queensland Herbarium.

Later he was told he had made the botanical discovery of the century. Stuart Worboys a botanist at the Australian Tropical Herbarium said “It’s the only member of its family in the Southern Hemisphere and its restricted to about 2300 hectares of the Wet Tropics World Heritage Area in the Daintree. Because its so divergent from most other plants it greatly increases the biodiversity of the Wet Tropics”.

Idiot Fruits lifecycle leaves us with some questions about seed dispersal. It has many unique features that may once upon a time been commonplace in plants. Its seeds are large, heavy and don’t float they are also very toxic. This makes it very hard for new trees to sprout away from parent trees. Seeds seem to only spread by gravity so can only get some distance from their parents if they roll downhill. Probably why the trees are now only found in very wet lowland rainforest and in only a few locations. Fossils of idiot fruit show that it was around very early on in the age of angiosperms more than 120 million years ago when there were dinosaurs living on the earth, they probably were recruited by the trees for seed dispersal. Another characteristic that sets this tree apart from all other modern flowering trees is that modern trees sprout from seeds in two ways. They are either monocots one seed leaf from a sprout or dicots with two seed leaves from sprouting. Idiot fruit can have from two to six seed leaves from sprouting and they can even have multiple sprouts from one seed, up to five have been recorded. Flowers are cream to red and arranged in spiral whorls another primitive characteristic. It’s flowers also produce a pungent odour to attract flies which are the principle pollinators of most primitive flowering plants. As well as being toxic with a poison not unlike strychnine the fruit is large at about 80mm long (about the size of a fist) and globular in appearance they split into four segments when they hit the forest floor. Seeds are the largest single seeds in Australia. Seedlings can be 80cm to a meter tall for a long time many years in the understory patiently waiting for a break in the canopy and sunlight to reach them so they can take their place amongst the forest trees and reach the canopy above.