Plant Diversity - The Green Dinosaur

The Green Dinosaur is one of the common names for this tree, also known as Ribbonwood and Idiot Fruit. It has its own interesting story of life, extinction and rebirth as well as an unsolved mystery!

The Ribbonwood tree (Idiospermum australiense) is a relic species and has a most unusual characteristic which sets it apart from modern plants. All modern flowering plants produce seeds which have either one seed leaf (monocots) or two seed leaves (dicots) but the seeds of the Idiospermum can have between 2 to 6 seed leaves! Normally seeds will germinate and send up a single shoot but the Ribbonwood can sprout more than one shoot per seed. The fruit is large at 80mm (just over 3 inches) and globular, splitting into four segments on the ground. The red, spirally arranged flowers are also another indication of its primitiveness.

The Green Dinosaur was located in the late 1800's by timber cutters south of Cairns who brought it to the attention of a German botanist named Diels. By the time Diels returned to the spot where this tree was found, they had been clearfelled for sugarcane (one of the principal commercial crops of north Queensland). It was believed to be gone forever. However, in 1971, the species was rediscovered - not because someone identified the tree from its unusual tree-ring pattern - but because its fruit was turning up in the stomachs of dead cattle! We now know that its fruit is toxic.

There is another intriguing aspect to the Ribbonwood tree and that is how its seeds are dispersed. The successful continuance of most rainforest species depends on their seeds being dispersed away from the parent plant. The Green Dinosaur's seeds are large, heavy, do not float and are too poisonous for most animals to eat. Gravity dispersal may be why the Ribbonwood tree is only found in very wet lowland rainforest in very few locations.

Perhaps a clue to its distribution can be found by examining Idiospermum's long existence in the forest. The Tertiary period (from 2 million to 65 million years ago) was the age of the Australian megafauna but the Idiospermum would have developed earlier on in the Age of Angiosperms which started at around 120 million years ago. Perhaps the heavy seeds were distributed by a much larger animal which has since become extinct. Thus, the tree now persists only where gravity has allowed its seeds to fall and settle.

Thanks are extended to the Flecker Botanic Gardens slide library for the use of photos copyrighted by D.Warmington, P. Shanahan and G. Sankowski.