Idiospermum australiense, the sole species in the genus Idiospermum, is one of the most primitive flowering plants known, having lived in the Daintree Rainforest of Queensland, Australia for up to 120 million years. It is only found in very few locations of North Eastern Queensland (e.g. Daintree National Park) in the very wet lowland parts of the forest, where it grows in groups of 10-100 trees together (rather than scattered individuals). Common names include Ribbonwood and Idiot Fruit.
It is an evergreen tree, growing to 20–30 m tall. The leaves are produced singly, in pairs or in whorls of 3-4; the leaf is simple, 12–25 cm long and 5–9 cm broad. The flowers are 4–5 cm diameter, with all floral organs spirally arranged (Staedler et al. 2007). The petals are initially creamy white when the flower opens, then turn red as the flower ages. The "fruit" is very distinctive and is not a fruit as such: all the protective layers decay and what is release from the plant it is an extremely large (8 cm in diameter) naked plant embryo. This is one of the very largest embryos in flowering plants. The latter is very toxic, inducing symptoms (in cattle) similar to strychnine.
Plants have both male and female sex organs, but half of the flowers of the Ribbonwood do not produce any fertile female organs (Staedler et al. 2009). Attracted by the sent and colour of the flower, small beetles and thrips are the main floral visitors (Worboys and Jackes 2005); they crawl in and lay their eggs within the center of the flower, which contains the flower's pollen. Within the flower some of the sticky pollen gets trapped on the insect's bodies, and if the next flower they visit is a receptive one, it will pollinate and produce the seeds.
While most modern flowering plants produce seeds which have one cotyledon (monocotyledons) or two (dicotyledons), the seedlings of the Ribbonwood have between two and five cotyledons. Also the Ribbonwood can produce more than one shoot per seed (usually one per cotyledon).
The seeds are currently mainly spread through gravity dispersal, the seeds rolling down the steep mountain slopes to find their new home. The seeds are so toxic that most animals cannot eat them without being severely poisoned; however it is known that the native Musky Rat-kangaroo does disperse and bury some of these seeds. It has been suggested that the seeds were formerly dispersed by the now-extinct Diprotodon, on the basis that many Australian marsupials are adapted to cope with the toxins in Australian plants.
The plants have adapted a unique poison, a chemical called Idiospermuline contained within the seed, to prevent animals eating them. Researchers discovered the poison affects transmission of messages between individual nerve cells, which may cause seizures. In small doses this chemical can be used to save lives.