|
Coconut Palms |
 |
To many people, the words 'coconut palm' conjure up a vision of tall waving trees fringing a sandy shore under brilliant blue skies. In fact, coconuts (Cocos nucifera) are found throughout the wet tropics between the latitudes 20° north and south of the Equator. They do often grow on sandy beaches because conditions there are ideal for them: a humid atmosphere, a temperature of 27-30°C, a free-draining well-aerated soil and a supply of fresh groundwater. No-one really knows where coconut palms originated, although wild specimens have recently been found growing in natural coastal forest in the Philippines and Australia. These finds support the theory that the coconut arose somewhere around the western Pacific. From there, it was probably distributed to both east and west by sea (the coconut can still germinate after some considerable time in seawater) and, more especially, by early people; it had reached the Americas before Columbus arrived there in 1492. |
Characteristically, the coconut palm has a tall unbranched trunk surmounted by a crown of fronds, although branched forms are occasionally found. The light grey trunk is ringed at intervals by leaf scars. From its swollen base (bole) adventitious roots arise - these are strong enough to anchor the palm to the ground during hurricanes and typhoons. Older leaves typically have leaflets (pinnae) on either side of a central stem in a feather-like arrangement, whereas in seedlings and buds the leaves are entire and unbroken. At the top of the stem the leaves surround a large apical bud. This edible bud is known as 'millionaire's cabbage' and is considered a delicacy, but its removal causes the tree to die as it is the only growing point.
Flowering begins after 6-7 years. Inflorescences (flowering heads) are borne in the leaf axils (where the leaf meets the stem). Initially two leathery leaf-like structures (bracts) protect each inflorescence. The branched inflorescence, which may be 2 m long, has separate male and female flowers. There are only a few female flowers on each inflorescence and these are found together with a pair of male flowers at the base of the branches; most of the male flowers are borne singly or in pairs towards the branch tips. As the flowers contain nectaries and are sweet scented, it is thought that they may attract insects for pollination. However, as the pollen is light and dry, there may also be some wind pollination. The male flowers mature and wither before the female flowers become receptive (a condition known as protandry) so that flowers in the same inflorescence cannot pollinate one another. This ensures cross-pollination. The coconuts available in this country are only part of the coconut fruit. When first collected from the tree, they still possess their outer layers: a smooth skin ranging in colour from green to brown around a fibrous layer, which is used commercially as coir. These layers surround the hard dark-brown shell, which encases the coconut seed. The outer layer of the seed, the testa, is the brown papery material that adheres to the white flesh (endosperm) when it is removed from the shell. Coconut water (sometimes, misleadingly known as coconut milk) fills the cavity in the centre of the coconut and can be used as a refreshing drink. |
 |
The coconut has been described as 'one of Nature's greatest gifts to man' because almost every part of the tree is used in some way. Coconut oil, extracted from the dried endosperm (copra), is unusual amongst plant oils in that it is solid below 24°C. In the early days of margarine manufacture, it was one of the major raw materials, as it was considerably cheaper than animal fats. It is still widely used to make soap and cosmetics. Dessicated coconut is produced by shredding the dried endosperm. Coconut milk and cream, often required for cooking curries, are prepared by soaking either the fresh or dried endosperm in warm water and then filtering away the solid material; the cream rises to the surface of the milk if it is left to stand.
Other uses of the coconut range from the production of an alcoholic drink to building materials. By tapping the unopened inflorescence, a sugary sap called toddy is collected. This can be drunk as it is, or fermented and then distilled to produce the fiery spirit, arrack. The fibrous coir removed from the husks of the coconut is used to make ropes, nets, mats and brushes and is particularly useful as it is resistant to water. Coir waste is now being used in horticultural composts. Whole or half shells are often polished and decorated for use as utensils or ornaments. The trunks can be used for building and the leaves are plaited for thatching.
Imported coconuts will sometimes germinate but removal of the husk makes this unlikely. Fresh seeds should be placed on damp peat with the broadest surface downwards at a temperature of 24-27°C. The seed germinates slowly, taking up to 4 months before the shoot appears. During germination, the single cotyledon (seed leaf) grows inside the seed cavity. Its sheath protects the seedling root and shoot and grows with them through the softest of the three eyes at the base of the shell. Part of the cotyledon, the coconut apple, enlarges into the cavity inside the coconut and absorbs nutrients from the endosperm and coconut water. Because the seedling has access to this food source, it can grow for some time before making contact with the soil.
Seedlings still attached to the coconut can be obtained from some suppliers. These will survive for a few years but do not make ideal house plants as they require constant high humidity and temperatures. They should be grown on a well-drained sandy soil rich in lime and potash. Seedlings with the seed attached should not be transplanted until the connection with the seed has shrivelled. In containers coconuts may be expected to reach up to 2 m in height with pinnate leaves of a similar length.
Despite its name, the double coconut (Lodoicea maldivica) is not closely related to the coconut. It is named after its immense fruits which resemble pairs of coconuts joined together. Its seeds are the largest in the plant kingdom. The tree grows wild on only two small islands of the Seychelles group and may reach up to 25 m in height. It has a crown of heavy fan-shaped leaves and male and female flowers on separate trees. Another name for the double coconut is the coco-de-mer because for several centuries it was only known from the appearance of its fruits as flotsam cast up by the sea.
Coconuts and double coconuts can both be found in the Palm House.
Child, R., 1974. Coconuts, 2nd edn., Longman
Cobley, L. S., 1976. An Introduction to the Botany of Tropical Crops,
Longman
Keesing, J. S., 1988. Useful plants. In The Kew Gardens Book of Indoor
Plants, ed. J. B. Simmons, pp. 186-213, George Philip
Ohler, J. G., 1984. Coconut, the tree of life, Food and Agriculture
Organisation
Purseglove, J. W., 1968. Tropical Crops: Monocotyledons, Vol. 2,
Longman