Idiospermum

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Idiospermum
Gardenology.org-IMG 0431 rbgs10dec.jpg
Habit in cultivation
Scientific classification edit
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Magnoliids
Order: Laurales
Family: Calycanthaceae
Genus: Idiospermum
S.T.Blake
Species:
I. australiense
Binomial name
Idiospermum australiense

Idiospermum is a genus containing a single species of tree, Idiospermum australiense, found in Australian tropical rainforests. The species represents one of the earliest known lineages of flowering plants, dating back as far as 120 million years. It is found today only in the Daintree and Wet Tropics rainforests region of north-eastern Queensland. It is endemic to a very few locations in north-eastern Queensland (e.g. in Daintree National Park), in the very wet lowland parts of the forest, in groups of 10–100 trees together (rather than scattered individuals). Common names include ribbonwood and idiot fruit.[1]

Description

Ribbonwood trees grow naturally in their wet tropical rainforest habitats as evergreens up to about 20–40 m (70–130 ft) tall and about 90 cm (35 in) in diameter at breast height (DBH). The simple leaves grow singly, in pairs or in whorls of 3–4, each one measuring about 12–25 cm (5–10 in) long and 5–9 cm (2.0–3.5 in) wide. The flowers measure 4–5 cm (1.6–2.0 in) in diameter, with all floral organs spirally arranged.[2] The tepals are initially creamy white when the flower opens, then turn red as the flower ages. The "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 (8 cm (3.1 in) diameter) naked plant embryo.[3] This is one of the largest embryos of any flowering plant. It is very toxic, inducing symptoms in cattle similar to those of strychnine poisoning.[4]

Trunk in cultivation
Leaves and trunk in cultivation
Flower starting to open
'Idiot fruit' seedling

Reproductive organs

Plants have both male and female sex organs, but half of the flowers of the ribbonwood do not produce any fertile female organs.[5] Attracted by the scent and colour of the flower, small beetles and thrips are the main floral visitors.[6] 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). I. australiense is the only known species in which the flowers display a continuous spiral series of bracts, sepals, petals, stamens and finally staminodes.

Seeds and their dispersal ecology

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.[citation needed]

Etymology

The name Idiospermum derives from the Ancient Greek idios meaning individuality or peculiarity, and spérma meaning seed, referring to the unique characteristics of the fruits. The common name "idiot fruit" is a mistranslation of this.

Scientific recognition

The first European-Australians to recognise the trees were timber cutters south of Cairns in the late 1800s. It was thought to have become extinct, but was later brought to the attention of the German botanist Ludwig Diels, who in 1902 described the species in the genus Calycanthus as C. australiense, a remarkable disjunction for this otherwise North American genus. It was later believed to be extinct again, because when Diels finally returned to the location where this tree was found, the natural vegetation had been destroyed for a sugar cane farm.

In 1971, John Nicholas, a Daintree grazier, believing someone to be poisoning his cattle, called in the police. A government veterinarian, Doug Clague, discovered in the cows’ stomachs relatively intact Idiospermum seeds that had been swallowed whole. Curious about this seed’s ability to kill cattle—after first causing spasms and paralysing the nerves—he sent specimens off to botanist Stan Blake at the Queensland Herbarium.

Upon receiving the specimen Blake recognised the outside shell of the fruit as belonging to the same plant which had been previously described by Ludwig Diels as Calycanthus. Blake was eager to undertake a detailed study of the plant and requested that ecologists Len Webb and Geoff Tracey of the CSIRO Rainforest Ecology Research Unit, who were to shortly embark upon a research trip to the region, stop at Cape Tribulation for the purpose of locating a complete intact set of specimens.

Upon arriving in the Daintree area Webb and Tracey stopped at a small watercourse called Oliver Creek, a short distance south of Cape Tribulation, where they were soon able to locate a number of the trees in full flower amidst the riparian forest. They collected samples of the plant including a piece of bark as well as samples from other trees with which they were unfamiliar. These included a number of species which had not previously been recorded in Australia such as Ryparosa javanica and Gardenia actinocarpa as well the then undescribed Lepiderema hirsuta.

Upon analysis of the bark sample that Webb and Tracey had collected at Oliver Creek, chemists were able to isolate an alkaloid called Calycanthine which initially suggested that Stan Blake was correct in his assumptions about the identity of the plant. Upon closer inspection of the fruit and the flower specimens together, along with details of the size of the tree, it soon became apparent to Blake that the poisonous fruit did not belong to a Calycanthus despite it being a part of the Calycanthaceae family which represents a very primitive line of angiosperms.

Blake determined that the specimen was so different from the rest of the Calycanthaceae family that a new genus called Idiospermum was erected with Idiospermum australiense as the sole species. [7][8]

References

  1. ^ (Hyland et al. 2010)
  2. ^ (Staedler, Weston & Endress 2007)
  3. ^ (Staedler, Weston & Endress 2009)
  4. ^ (Hyland et al. 2010)
  5. ^ (Staedler, Weston & Endress 2009)
  6. ^ (Worboys & Jackes 2005)
  7. ^ Heathcote, Angela. "The Idiot Fruit Tree". Australian Geographic. Retrieved 2 January 2021.
  8. ^ Tracey, J. G. (John Geoffrey); Borschmann, Gregg (1994), John Tracey interviewed by Gregg Borschmann in the People's forest oral history project, pp. 41, 42

External links

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