Green Culture Singapore Feature Article for September 2006
	Pictures from National Parks Board (NParks)
	Text by Prof. Wee Yeow Chin
	(Patron of the Singapore Gardening Society)
	Online on 30 Sep 2006

I am sure most, if not all readers are all familiar with the frangipani (Plumeria obtusa, P. rubra). Isolated trees can still be found in gardens and parks and definitely in the Singapore Botanic Gardens where many cultivars and hybrids are grown. Older gardeners may not care to have these trees in their gardens as they are associated locally with funerals. The white frangipani flowers were once used to make wreaths. The tree was also popular in Muslim cemeteries as it is free flowering and the daily shedding of flowers was taken as floral offerings to the dearly departed. The Hawaiians similarly used to shun frangipani because of its association with graveyards. Not so now! The flowers are commonly used to make leis. And do you know that P. obtusa, is commonly referred to in Hawaii as Singapore plumeria? Actually the plant originated from the West Indies but a cutting was taken from Singapore to Hawaii in 1931 and since then the plant has been known by this name.

Above left & right: Flowers and habit of Cerbera odollam. Below left & right: Flowers and habit of Thevetia peruviana.

I am also sure that most readers would be familiar with pong pong (Cerbera odollam). It was once commonly planted along many local roads, so much so that it got the name of Singapore apple. Then there are the yellow bells of allamanda (Allamanda cathartica), the Madagascar periwinkle (Catharanthus roseus), the oleander (Nerium oleander) and the yellow oleander (Thevetia peruviana). These are also familiar garden plants many of us grew up with. Now what have all these plants in common? If you break off a leaf, white latex oozes out. The flowers are always colourful. The parts are in fives - sepals, petals and stamens. The petals are bell or funnel-shaped, joined at the lower portion but with the five lobes always distinct. Leaves are always simple and arranged in pairs or in whorls. Fruits are generally a pair of follicles, each splitting open at maturity along one side only to liberate the seeds. All these characters unite the above plants as well as many others into a distinct botanical unit, the family Apocynaceae. By agreement family names always end in -aceae or -ae so that it is easy to recognise them as such. Within the family are genera, like Plumeria, Allamanda and Cerbera. Thus genera are a lower sub-set of the family and species (sp. or spp. in short), as in P. obtusa, A. cathartica and C. odollam are a further sub-set of the genus. Note that the genera are shortened when the plant has been earlier mentioned. Also, botanical names are traditionally written in italics, as these are not the usual English words.

Left: Allamanda cathartica; Middle: Catharanthus roseus & Right: Nerium oleander.

Members of the Apocynaceae are mostly tropical plants, represented by trees, shrubs, herbs and climbers, including large woody lianas commonly seen in the forest. A number of forest trees from this family have commercial value. Jelutong (Dyera costulata) and pulai (Alstonia spp.) produce a lightweight hardwood used to make pencils, drawing boards, matches and packing cases. The latex of jelutong can be used to make chewing gum while that of pulai is used medicinally. In the days before para rubber, the latex of the former was also used as a source of low grade rubber.

Above left & right: Leaves and flowers of Dyera costulata. Middle left & right: Leaves and habit of Alstonia angustiloba.

The family is also well known for the alkaloids they contain, many of which are poisonous, a number of which have since found their way into modern medicine. A good example is the Madagascar periwinkle. This herb is the source of two important alkaloids, vinblastine and vincristine. The former is used against Hodgkin's disease while the latter to control acute lymphocytic leukemia in children. Traditionally this plant had been used in Madagascar and Jamaica for diabetes. So far, more than 100 alkaloids have been isolated from the plant.

Another well-known medicinal plant is the Indian snakeroot (Rauwolfia serpentina). For centuries Indians used the roots to treat the mentally ill, to expel intestinal worms, to treat dysentery and to cause uterine contraction and thus promote expulsion of the foetus. It was only in the early 1950s that the plant found its way into western medicine as a treatment for mental illness. Chemists subsequently isolated about 50 alkaloids from this plant, the most common being reserpine. Reserpine has tranquilising and antihypertensive properties and is made used of in modern medicine today.

Above left & right: Habit and flowers of Strophanthus gratus.

The strychnine tree (Strophanthus spp.) is a common source of arrow poisons in Asia and Africa. The seeds are very poisonous as they contain the cardiac glycosides, strophanthins. These chemicals have now been incorporated into western medicines to treat heart diseases. In Turkey extracts of oleander are used to treat cancer. The Indians once used such extracts to treat leprosy, to induce abortion and to kill lice. The Indians also consider allamanda bark an excellent laxative. So do the Cubans who drink the latex or a tea made from the leaves. The Colombians once drank the latex to expel intestinal worms. However, traditional use of many apocynaceous plants can be dangerous, sometimes even leading to death. Gardeners should be extra careful when handling members of this family. Make it a point to wash your hands always, as accidental contact of the latex with the eyes can result in great discomfort. Also, any latex entering the body through open cuts and wounds can cause serious problems. Again, a number of these plants are downright poisonous, containing in their latex cardiac glycosides and poisonous alkaloids. With oleander, the leaves and flowers are highly poisonous. In fact, it has been recorded that many of Alexander the Great's soldiers died after using oleander twigs to barbecue meat. But we need not delve into history for such an example. Some years ago in Hawaii, a person died after eating meat that was skewered on an oleander branch and cooked over an open fire. There have also been cases of people getting sick through inhaling smoke from burning leaves and branches of the plant. Water contained in vases where oleander flowers are placed is also poisonous. A woman in California died about 10 hours after drinking tea made from oleander leaves she apparently mistook for eucalyptus leaves. In Florida children have been known to develop symptoms of heart failure after licking the latex from their fingers. Happily, we have not seen any such poisoning in Singapore.

Yellow oleander can be just as dangerous as oleander. Although cardiac glycosides are found in all parts of yellow oleander, the seeds have the highest concentration and a single seed can cause the death of a child. The seeds of pong pong have been used in our local schools to poison rats.

One species is used as a hallucinogen. This is the African iboja (Tabenanthe igoga), a shrub whose roots contain the psychoactive indole alkaloid, ibogaine. The natives, especially members of secret societies in Gabon and the Congo, grind pieces of roots into a powder and swallow it with water. After some time they fall into a trance and thus are said to make contact with their ancestors. In this way sorcerers seek information from the spirit world and chiefs take advice from their ancestors. The alkaloid imparts on them extraordinary physical stamina, a feeling of lightness and various sensations involving smell, taste and technicolour vision.