Palms are a large group of trees constructed on a peculiar plan, which makes them look, quite simply, like a huge tuft ofset at the top of a long pole. They evolved about ioo million years ago under tropical climates, and with few exceptions, cannot tolerate frost. Nearly all the 3,500 different species are confined to the tropics, hence palms have become symbolic of hot climates.
Structure and life pattern
Botanically, palms belong to the subclass Monocotyledones, that is, they have only one cotyledon, or- , within each seed. In the palms, this does not emerge itself from the seed-coat, instead it nourishes a stalk that emerges and sends down the first to gain water and mineral salts from the soil. At the upper end of this stalk a bud develops to become the starting point of the palm’s upright . This stem bears juvenile which are different in form from those of an adult palm. They look rather like broad blades of grass, or the leaves of the wild plantain weed, Plantago lanceolata. True leaves come later. All palm leaves develop at the tip of a single stem for, with few exceptions, palms never bear side branches.
Palm leaves are of two main types, according to species. Some, the fan palms, have a broad spreading blade, which may, or may not, divide into radiating arms; it is usually carried on a long tough stalk. Others, the pinnate or feathery-leaved palms, have a compound leaf with a long central stalk and many side leaflets. Both develop in the same way, from a leaf element that grows at its base, not at the tip as in broadlcaved trees. Palm leaves are protected as they emerge by a large leaflike sheath, which later bends down and falls away. Leaves always expand in strict succession, with the youngest and smallest at the tip, older ones below, in a spiral down the stem. They appear at regular time-intervals of a few weeks. Some reach enormous size, up to 5m (15ft) long on feathery-leaved palms.
Palms are evergreen, and each leaf lives for several years. Eventually it turns yellow, its stalk bends outwards and downwards, and it dies. Certain palms carry a ‘skirt’ of dead, drooping leaves down their trunks for many years; others drop their dead leaves but keep the bases of the stalks, and others again develop clean.
Because growth is only possible from the soft bud at the tip of the stem, any major injury to it means the death of the tree. The stalks of the leaves that surround it are therefore armed with sharp spines, which discourage browsing animals, such as jungle tapirs; some spines point one way, some another. The soft shoot of the coconut palm, which is good to eat, is protected by law in many countries, to ensure the survival of a valuable food source.
The woody stems of palms are built up in quite a different way to those of cither broad-leaved or coniferous trees. They consist of fibrous bundles of conductive tissues, set within a hard outer cylinder. Some of these bundles carry upwards the root-sap which consists of water and dissolved minerals. Others carry downwards the leaf-sap, with its sugars or carbohydrate foods, obtained byin the leaves. The two elements run side by side, in spiral paths from leaves to . There is no central cylinder of hard wood, no cambium tissue to effect secondary thickening of the woody stem and no growth rings. Hence, with a few exceptions, such as the African oil palm, the trunks of palms never get thicker. They remain the same diameter from base to top.
Palm leaves have parallel veins that run from the stalk to the edge. There are no branching veins spreading sideways, such as occur in broadleaved trees. If a leaf is broken into segments by the wind, as often happens, these segments continue living just as before.
There are no large woody roots at the base of palms. Instead, small roots made of bundles of fibres, rather like those seen on flower bulbs, radiate out through the soil from the base of the tree. These roots are immensely strong, and though leaning palms are common, it is rare to see any palm blown over through root failure, even on coasts exposed to hurricanes.
Palmseldom attract notice, for they are usually borne in the central tuft of leaves high up the stem; a few kinds have flower spikes lower down. Some palms bear flowers with organs of both sexes. More usually male flowers open in clusters separate from those of female flowers, but on the same tree; date palms are an exception, being either all-male or all-female. Each inflorescence is protected in bud by a large leafy sheath called a spathc, which falls away later. As is effected by wind there are not bright petals to attract insects, no scent and no nectar. Each inflorescence is branched and carries a large number of separate flowers, each with three green rudimentary sepals and three green rudimentary petals. Male flowers have six stamens each. The female flowers have a pistil likewise divided into three sections, from tip to base. They sometimes bear three, or more, , but usually only one completes its development.
Most palm fruits are single-seeded, so fruit and seed may be described together. Some, like coconuts, are hard nuts that develop in a fibrous outer husk. Others, like dates and oil palm fruits, are plumlike, and consist of a hard stonelike seed, surrounded by sweet or oily pulp. Many are spread by birds or beasts, but some, like the coconut, float and are carried by water, even across oceans. Palm nuts are naturally brown or black, but the soft fruits are more colourful—yellow, red, blue, white or purple.
Under tropical climates many palms have no special seasons for growing, flowering or fruiting. They produce new leaves, open flowers and ripen fruits, at regular intervals of a few weeks, the whole year round. A few excep- tional palms, including the sago palm, postpone flowering for several years, then put all their resources into the growing of a huge central flower spike; this exhausts the tree, which then dies. The most spectacular examples—exceptions to the general rule of rather insignificant flowers—are perhaps Corypha species, like the talipot palm, which produce an inflorescence 6m (20ft) tall estimated to contain 60 million flowers!
In the hot lands around the equator palms play major parts in natural vegetation under widely varying conditions. Though at first sight they look vulnerable to suppression by broadleaved trees, they hold their own in mixed forests; since they do not branch, they grow tall quickly. Some species, like date palms and carnauba wax palms, have low water requirements and thrive in regions with long dry seasons. Others, like the Malaysian sugar palm, tolerate marshy soils, and flourish along river banks even if submerged occasionally by floods. Coconut palms can live on salty sea-coasts. A fairly well-defined line runs round the globe marking the northern limit of spread for palms. In Europe, it starts in Spain, crosses the south of France near the coastline of the Riviera, and then crosses northern Italy below the Alps on its way east to Asia Minor and the Himalayas; several palms grow in southern China. In America, vigorous outdoor palms are limited to California, Florida and the neighbouring southern states. The hardiest known palm, the chusan or windmill palm, Trachycarpus fortune! from the mountains of South China, grows out-of-doors in sheltered places in southern
England. It bears fan-shaped leaves, and carries flowers and fruits regularly. Europe has one native palm, a low fan-shaped kind called Chamaerops humilis, found on dry hillsides facing the Mediterranean. There is also a form of date palm, Phoenix thcophrasti (perhaps the ancestor of the cultivated date), native in Crete, which is usually considered part of Europe.
Usefulness to man
In the regions where they thrive, palms prove exceptionally useful to mankind, in fact whole economies are based on them. They provide building materials, fibres, sticks and ropes, and a range of nutritious foods. The peculiar fibrous wood of palms, though sometimes praised in textbooks, is however only used where people cannot get anything better; it is soft and non-durable. The leaves, in contrast, are valuable for constructing and roofing houses. They are cut whilst green, dried in the hot sun and made up into flat panels called, in Malay-speaking lands, altaps. These are then used for serviceable windproof walls, and completely rainproof roofing thatch.
The coconut palm, Cocos nucifera, is the most widespread cultivated kind. Nobody knows where it first arose, for itshave been carried on ocean currents to every tropical seashore. The Caribbean zone of Central America is a possible starting point. The familiar hard round brown nut, commonly 15cm (6in) in diameter, ripens within a much larger oval husk, three times that size. This has a grey-brown leathery outer skin, enclosing a mass of tough grey fibre, and the whole provides an excellent float for a big water-borne seed. The fibre, known as coir, is widely used for making matting and cheap ropes. The inner surface of the actual coconut is lined with hard white oily ‘flesh’, and it also holds sweet white liquid ‘milk’, refreshing to the taste. Both substances are intended to sustain the when it sprouts on some dry salty beach. The shoot emerges through one of the three dark ‘eyes’, the other two being ‘blind’.
Coconuts are planted everywhere in the tropics beside homesteads, as a handy onthe-spot food supply. There are also big commercial plantations which produce copra, the sun-dried flesh obtained by splitting the nut. This is exported as a source of oil for soaps and margarine. An established tree ripens 50 nuts a year, in a steady succession, uninfluenced by the seasons. The huge feathery leaves, commonly 5m (16.5ft) long, spring from a tall slender stem up to 30m (98.5ft) high, often gracefully curved.
Date palms, Phoenix dactylifera, are adapted to the difficult dry climate of the Sahara and Arabian desert fringes, where they are scorched each day but face near-freezing temperatures by night. They need little water, but must have an assured supply from the springs of an oasis, a seasonal stream or a permanently flowing river. Date palms are rather stout trees, rising 20m (65.5ft), with rugged stems studded with bases of fallen leaves. These feathery-compound leaves, grey-green in colour, and often 3 m (10ft) long, curve gracefully, and provide welcome shade for desert-dwellers.
Each date palm is either wholly male or wholly female. The Arab grower, unwilling to waste precious water or soil on too many male trees that yield no dates, arranges their sex-life for them. He grows as few males as possible, climbs the trees in the flowering season, takes flowering branches from the males and shakes out their pollen in the crowns of the female trees. The plum-hke dates, borne in long-stalked clusters, have sweet nutritious oil-rich flesh and a hard grey central stone—the seed. Easily preserved by drying, they form a handy staple food. Date palms are increased by planting natural off-shoots which preserve the sex of the parent tree; once established, they bear fruit over long spans of years.
The West African oil palm, Elaeis guineensis, resembles the date palm but demands a much wetter climate, thriving best under year-round rains near the equator. Its datelike hard-stoned fruits ripen all the year round, and have an oily, rather than sweet, flesh. Oil palms are now grown commercially in many tropical countries for the palm oil that is expressed from both the soft pulp and the actual seed kernel. This is used, like coconut palm oil, for making soap and margarine; it is also a good source of food and cooking oil for local cultivators.
Sago palms, Metroxylon sagn, are grown on rich riverside land in Southeast Asia for the starchy food reserves that they build up in their soft trunks, in readiness for flowering and seeding. When, after several years’ rapid growth, they are about to flower, the grower cuts them down, splits the trunk and scrapes out the nutritious soft white starch. After washing, this is forced through a sieve and heated gently to make lumps of’pearl’ sago.
The Malaysian sugar palm, Arenga saccharifera, holds sap so rich in sugar that its leaf stalks can be tapped, as a source of syrup and sweetmeats. This and many other kinds, including coconut palms, are also tapped to obtain ‘toddy’, an alcoholic drink. An agile tapper climbs the tree and draws off sweet-sap from a flower spike— which in consequence never flowers. The sugar ferments within a few hours to a weak alcoholic drink; this can be distilled to give a strong spirit called arrack.
Raftia, widely used in basketry, consists of tough fibrous strips pulled from the leaves of a Madagascan palm, Raphia ruffia. Piassava, the far tougher fibre used in broom heads, is obtained from the leaf bases of a South American palm, Attalea funifera.
Rattans or canes, used both for basketry and the construction of cane furniture, are the stems of climbing palms, Calamus species, that grow wild in tropicaljungles. The shorter, more rigid Malacca-canes, used as walking sticks, are the stems of a dwarf Malaysian palm, belonging to the same genus.
The Brazilian carnauba palm, Copernicia cerifera, which opens large fan-shaped leaves in a climate with a long dry season, is the source of a wax used in polishes of many kinds. The palm develops the wax to restrict water loss. It is scraped from cut leaves and used to repel water in, for example, shoe polishes. ‘Vegetable ivory’, a hard white strong material used for carving buttons and ornaments, comes from the hard seed of certain palm trees, including the branching doum palm, Hyphaene tlieobaica, of East Africa, the coquilla nut tree, Attalea funifera, of Brazil, and the vegetable ivory palm, Phytelephas macrocarpa, also South American.
Many kinds of palms are grown in tropical and subtropical countries as ornamental street or garden trees. In places like the French Riviera, Italy, Florida, California and the Cape Province of South Africa, they give a richly romantic impression of tropical luxuriance. Fairly hardy fast-growing kinds, include the feathery-leaved Canary Island palm, Phoenix canariensis, the fan-leaved Californian washingtonia, Washing-tonia filifera, and the swollen-stemmed feathery-leaved royal palm, Roystonea elata, native to Florida.
In the central tropics, where frost never strikes, the decorative kinds include the striking sealing-wax palm, Crystostachos lakko, which has brilliant red leaf sheaths, and the slender-stemmed betel nut palm, Areca catechu. The latter is the source of the hard nuts that are sliced and chewed, along with a little lime and the leaves of the betel vine, Piper belle, by many Malaysians and Chinese as a stimulant, rather like chewing gum.
One of the oddest palms is the double coconut, Lodoicea maldivica, native only to the Seychelles Islands of the Indian Ocean. The huge heart-shaped seed weighs up to 25kg (55lb), the largest known for any plant, and takes six years to ripen. The fan-shaped leaves have stalks 10m (33ft) long and blades 5m (16.5ft) long by 2.5m (8ft) broad.