OVERVIEW OF BORNEO NUTMEGS
References: De Wilde (2000) Tree Flora of Sabah and Sarawak , Volume 3. and De Wilde (2000) Flora Malesiana Ser. 1 Vol. 14 .
In Borneo there are approx .115 species of nutmegs in 5 genera. All species are dioecious i.e. trees are either entirely male or female. Obviously only female trees produce fruit/seeds.
Endocomia: 3 species
Gymnacrantha: 5 species
Horsefieldia: 39 species (9 endemics)
Knema: 44 species (30 endemics)
Myristica: 20 species including the cultivated nutmeg illustrated above.
Dispersal ecology: All nutmeg fruit contain a single large dark colored seed. The seed is either totally or partly (lacinated) covered in a thin oily aril which is brightly colored usually red or orange. Prior to ripening the aril is protected by a thick pericarp. When the fruit is ripe the pericarp splits (dehices) longitudinally whilst the fruit hangs exposed on a tree, exposing the colorful aril. The aril covered seed varies in size but the largest seeds 2.5 x 7 cm can only be swallowed by a hornbill or an imperial pigeon.
Regurgitation: The oily aril is very thin and the seed itself is more or less toxic to most primates so dispersal is restricted to large birds which swallow the seed and aril together later regurgitating the seed without damaging it.
Double aril: Some nutmeg species in Borneo which occur next to riverbanks have a double aril. Under the colorful top aril is a second plain white aril tightly covering the seed. It is likely that this second aril remains intact even if the seed has been swallowed and regurgitated. The second aril makes the seed look like a fat white grub and likely aids secondary dispersal by fish in the river and perhaps by civets and mousedeer on land.
Seed Predators: In the canopy langurs are known to crunch up the seeds after scraping off the aril. Langurs are seed predators of unripe fruit seeds. Most Bornean fruit seeds are more or less toxic to animals. Langurs have a specialist digestive system which enables them to detoxify the toxins. At ground level the Argus Pheasant and the Malay Civet are known to specialize in eating toxic seeds which have fallen to the ground.