The Green Dinosaur (Idiospermum australiense) is one of the world’s rarest and most primitive flowering plants. Twice thought to be extinct, its rediscovery in the Daintree Lowland Rainforest in the 1970s was arguably Australia’s most significant botanical find.
Idiospermum - the Green Dinosaur
The Daintree Lowland Rainforest is home to one of the world’s rarest and most primitive flowering plants, known as the Green Dinosaur.
Idiospermum australiense, known as both Ribbonwood or Idiot Fruit Tree, was twice thought to be extinct. But its 1970s rediscovery in the Daintree has served to reinforce that the 1,200 sq km region known as the Daintree Rainforest is truly ancient and deserving of its status as the oldest continuously existing rainforest in the world.
Idiospermum australiense belongs to an ancient family of plants – more than 120 million years old. They are the most famous of the primitive North Queensland rainforest plants and are of great significance to science and to our understanding of how flowering plants have evolved.
The oldest known fossils of the tree date back 88 million years and this green dinosaur is often referred to as a “living fossil” due to its ancient lineage and the fact that it has remained relatively unchanged for many millions of years.
Fruit and seeds of the Idiospermum
Fast facts about the Green Dinosaur: Idiospermum australiense
- Idiospermum is a genus containing a single species of tree – Idiospermum australiense
- It was the discovery of Idiospermum australiense in 1971 inside the bellies of some dead cattle that brought international attention to the Daintree Rainforest
- The common name of this plant ‘Idiot Fruit’ is considered a mistranslation of the meaning of its genus name. Idiospermum derives from the Ancient Greek idios which means individuality or peculiarity. Sperma means seed
- Its seed is about the size of a human fist - one of the largest seeds of any Australian plant
- The flowers have characteristics that are considered primitive, including being spirally-arranged
- Flowers change colour as they age: they start off pale pink and slowly deepen to a crimson colour
- Unlike other Wet Tropics rainforest plants, the seeds are not dispersed by Cassowaries because they are toxic. Most other animals also cannot eat them without being severely poisoned. However, the endemic musky rat-kangaroo is thought to disperse and bury some of these seeds and seeds may have been dispersed in the past by the Diprotodon.
- They grow only in lowland rainforest between near sea level and 260m above sea level
Kelvin Davies inspecting the leaves of the Idiospermum
Distribution of Idiospermum australiense
The Idiospermum exists only in three geographically distant populations. One population is in the Daintree Lowland Rainforest below Thornton Peak and the other two are some 150km to the south, in the foothills of the Bellenden Ker range and Mt Bartle Frere.
These populations thrive in ‘environmental refugia’, which are habitats located near rain-attracting mountains that have remained climatically stable for millions of years.
This stability has allowed for the preservation of an extraordinary diversity of plants, including many primitive species, which have retained anatomical and genetic features similar to those of ancestral flowering plants.
Germinating Idiospermum seed
Timber-cutters were the first European-Australians to recognise the trees, south of Cairns in the late 1800s and it’s likely they gave the tree one of its common names – the ribbonwood. The tree was then thought to be extinct but it was later brought to the attention of German botanist Ludwig Diels who described the species in 1902.
When Diels later returned to the location where the tree was found, he discovered the vegetation cleared for a sugarcane farm and so the species was assumed, once again to be extinct.
In 1971 a Daintree grazier by the name of John Nicholas called in the police as he thought his cattle were being poisoned. Doug Clague was the government veterinarian who responded to that call. When he examined the cows’ stomachs, he found relatively intact Idiospermum seeds that had been swallowed whole.
This sparked some curiosity as to the seed’s ability to kill cattle – first causing spasms and then paralysing the nerves. Queensland Herbarium botanist Stan Blake was sent specimens of the seed and recognised the outside shell of the fruit as belonging to the same plant which had been previously described by Diels as Calycanthus. This prompted Blake to request a detailed study of the plant.
Len Webb and Geoff Tracey were ecologists at the CSIRO Rainforest Ecology Research Unit at the time and they were charged with a research trip to locate a complete set of specimens. They located a number of trees in full flower amidst the riparian forest at Oliver Creek, just south of Cape Tribulation. They collected samples that confirmed assumptions about the plant’s identity and that it represented a very primitive line of angiosperms.
It was determined that the specimen was so different from the rest of the Calycanthaceae family that a new genus was warranted and so Idiospermum was erected with Idiospermum australiense as its sole species.
“The discovery of Idiospermum fruit in the stomachs of dead cattle in the Daintree is arguably Australia’s most significant botanical find.”
Idiospermum australiense grows to a height of 40 m
Idiospermum leaves and trees
- Idiospermum australiense trees grow to 20 – 40m tall and about 90cm in diameter at breast height
- Idiospermum australiense leaves measure about 12 – 25cm long and 5 – 9cm wide. Simple leaves grow singly, in pairs or in whorls of 3 – 4
Idiospermum australiense flowers
- Flowers appear in June and July
- Flowers measure 4 – 5cm in diameter
- Floral organs are spirally-arranged
- When the flower opens, tepals are initially creamy-white
- As Idiospermum flowers age they change colour – first to a pale pink, then slowly deepening to a crimson
Idiospermum flowers (Photo CSIRO)
Pollination of Idiospermum australiense
Small beetles and thrips are attracted by the flowers’ scent and colour. They crawl in and lay their eggs in the centre of the flower, which contains the flower’s pollen. This is then transferred to the next flower they visit.
While most modern flowering plants produce seeds which have one cotyledon (monocotyledons) or two (dicotyledons) the seedlings of the Idiospermum can have between two and five cotyledons. The Idiospermum can also produce more than one shoot per seed (usually one per cotyledon). It is the only known species to display a continuous spiral of bracts, sepals, petals, stamens and staminodes.
Fruit and seeds of the Idiospermum
Idiospermum australiense fruits and seeds
Idiospermum “fruits” have very distinctive features and do not fit within the definition of true fruits as such: all the protective layers decay while still on the parent tree and each one released is an extremely large naked plant embryo.
These plant embryos or seeds can measure 8cm in diameter which is considered very large and certainly is the largest single seed of any Australian plant.
Idiospermum seeds are globular and split into three, four, and occasionally more, segments when on the ground. The starchy reserves in the enormous seeds provide the energy for the seedlings to establish in the low light of the rainforest floor, reaching up to 1m in height.
Germinating Idiospermum seed
Dispersal of Idiospermum australiense
Unlike other rainforest fruits, Idiospermum seeds are not consumed and dispersed by the Southern Cassowary. This is because the seeds are very toxic, inducing symptoms in cattle similar to those of strychnine poisoning. Musky-rat kangaroos are known to scatter-hoard seeds and fruits from a variety of tropical plants and trees. It is thought that this species may disperse and bury the seeds of the Idiospermum australiense.
Some specimens are located near creeks however the seeds do not float.
Gravity does its work - they fall from the tree and germinate where they come to rest, always very close to the parent tree. For this reason, they are only found in groups of 10 to 100 trees together (rather than scattered individuals) with all seedlings close by.
The tree's evolution can be traced back to the Age of Angiosperms, which started around 120 million years ago. During this time, a much larger animal might have dispersed the seeds, which have since become extinct. It has been suggested that the seeds were formerly dispersed by the now-extinct Diprotodon.
Lot 150 Cape Tribulation Road
A significant find
Our purchase of freehold land in the Daintree Lowland Rainforest ensures populations of rare and threatened plants and animals are managed for conservation.
We were thrilled to find a population of the Idiospermum on Lot 150 Cape Tribulation Road at Diwan, a property we have acquired for inclusion in the Daintree National Park (CYPAL). This is a freehold property created through a subdivision of land for rural residential development in the 1980s. We have surveyed the vegetation on 30 properties over the last three years and this was the first time we recorded the occurrence of the Idiospermum.
Thanks to Steven Nowakowski for many of the photos on this page
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