World Heritage listing of the Wet Tropics of Queensland in December 1988 was a conservation endorsement of the highest order that included a range of tenures including freehold land. Never before or since, has Australia imposed a conservation imperative of international dimension on freehold land. It was the discovery of the green dinosaur, Idiospermum australiense, in 1971 inside the bellies of some dead cattle that brought international attention to the Daintree Rainforest. Isolated relictual Gondwanan pockets containing an exceptional range of primitive flowering plants, called angiosperms, were subsequently discovered in Queensland’s wet tropical rainforests. At the time of the discovery, the world knew of 17 families of angiosperms. Two new finds Idiospermum australiense and Austrobaileya scandans became the only representatives of the 18th and 19th families. Twelve of these nineteen families are found in the Daintree Rainforest.
Such a concentration of primitive flowering plants cannot be found anywhere else on earth. The highest concentration of Idiospermum australiense is located in the Daintree Rainforest lowland flats at the base of the eastern flank of Thornton Peak, known as Wundungu to the Traditional Owners. It is here in pristine old growth rainforest, that the story of the rediscovery of the “idiot fruit” is recounted to travellers from around the world who visit Daintree rainforest to participate on a Cooper Creek Wilderness guided interpreted tour.
Through international co-operation, Australian scientists were able to piece together the story of original discovery of the seed in an area south of Cairns in 1902. German botanists, funded by the Humboldt Institute, were sent to remote places around the world to collect and catalogue rare and unknown plants. Botanist Ludwig Diels came to Northern Queensland, found some unidentified flowers in a rainforest area south of Cairns and transported them back to the Dresden Herbarium for analysis. Through comparison with fossil records Diels classified the plant as an unknown member of the Calycanthaceae family, the first to be discovered in the southern hemisphere. Diels needed a second sighting to corroborate his discovery, but clear felling of large tracts of rainforest for sugar cane thwarted further exploration of the area where the seeds had been discovered and so the plant was not officially classified until its rediscovery in 1971.
For a plant that has known extraordinary stability and continuity over an estimated 170 million years, scientific classification of Idiospermum australiense has had a checkered career. TS Blake is credited with the rediscovery in 1971, with the help of the dead cattle, and he erected a new family, Idiospermaceae for the new species that he named Idiospermum australiense. Its separation from the northern hemisphere family Calycanthaceae has always been contentious and with the benefit of DNA testing, the Green Dinosaur has been returned to the original Calycanthaceae Family maintaining the name Idiospermum meaning unique seed, one of a kind and australiense, only found in Australia. It was akin to discovering a dinosaur that was thought to be extinct. It was a green dinosaur of the plant kingdom. The trees themselves are alive and thriving in the Cooper Creek catchment where their concentration appears to be at its greatest.
It was well known to the timber community as “ribbonwood,” a good cabinet timber and following the rediscovery in 1971, scientific groups scoured the area around Cooper and Noah creeks, little knowing that the ribbonwood trees that were being chopped down were the “green dinosaur.” The area south of Cairns where the rediscovery occurred was soon to be cleared for sugarcane. World Heritage listing has secured its protection on State timber reserves that were dedicated to cutting down for their cabinet timber values and on the freehold portions that were included in the nomination. A thesis submitted by Stuart Warboys to James Cook University in Cairns in November 1998, entitled “Pollination processes and population structure of Idiospermum australiense (Diels) S. T. Blake, a primitive tree of the Queensland Wet Tropics.” has contributed substantially to the body of knowledge surrounding this tree, however there still remain many unknowns. They large round seeds germinate around the base of their parent trees, their rate of growth retarded by the shadow of its parent. There are no known vectors, but several conjectures over the years.
After much debate, it was concluded that the “Green Dinosaur” is one of the most primitive groups of flowering plants on earth with no other close relatives in the Southern hemisphere. It has extremely high conservation significance among the plants of Australia’s Wet Tropics. Its current distribution is limited to creek catchment areas at the base the three granitic inselbergs in the Wet Tropics section of the Great Dividing Range of Australia. Cooper, Hutchinson, Noah and Oliver Creeks in the closed lowlands rainforests of Thornton Peak, Harvey Creek near Mount Bellenden Ker and Russell River to the south of Mount Bartle Frere are refuges for these plants.
Distinct differences exist between trees in the northern catchments and those in the southern catchments indicate that an obstruction formed that prevented cross-fertilisation between north and south populations causing separate speciation. Most significant is the occurrence of hermaphrodite flowers (having both male and female) features in the south, while in the north less than half of the trees are hermaphroditic. The flowers are approximately 35mm in diameter, have hemispherical bracts that open to allow creamy-white petals to show. These petals darken through pale pink, to deeper pink to cerise over two weeks and are seen on the forest floor around June-July, the driest time of the year. Beetles pollinate the flowers, which is appropriate to primitive species. Seeds drop onto the forest floor between January and April, but not annually. Fruiting coincides with the wettest time of the year to facilitate establishment of the seedlings. The large fruit, weighing approximately 225gms does not appear to have a vector, although it may be aided by gravity. The corky receptacle around the fruit breaks open and probably cushions the fall. Most fruit are segmented into 3 or 4 cotyledons, but this is not fixed and can be any number from 2 to 7.
The Southern Cassowary is an important disperser of seeds in the rainforest, with 37 different species requiring transmission through the big bird’s digestive tract to facilitate germinate, and a further 200 or more seeds being more likely to thrive if transported away from the parent trees that may retard their growth. The Cassowary does not eat Idiospermum australiense. Even with its huge liver and ability to detoxify, the cassowary shuns the big seeds containing alkaloids calycanthine and idiospermuline that cause convulsions. A tour with expert inhabitants in Daintrree Rainforest is inspirational, not just for the unique sightings of the green dinosaur, but for the grandeur and beauty of fan palm dominated relictual Gondwanan rainforest. This is just one of the jewels in the World’s oldest rainforest.
