by Colin Tudge
The thirty-five families of the order Malpighiales include a great variety of truly remarkable trees both tropical and temperate: the rubber tree, the cactus-like euphorbias, the red mangroves, the willows and poplars, and some formidable American and African hardwoods. Some are of huge ecological significance, some are the basis of important industries, and some are just very strange. Three families in particular are outstanding.
The family Euphorbiaceae is truly extraordinary. It includes the herbs known as spurges, common as wayside flowers and beloved of gardeners. It also includes the finest range of cactus look-alikes: some are an almost perfect imitation of the Cereus-style cacti, having dark-green succulent columns with spiky ridges – almost uniquely goat-proof, and much favoured for hedges in Africa. Cassava or manioc, Manihot esculenta, is a major, starchy staple throughout the tropics. The shrub Ricinus provides extremely valuable castor oil. The oil of Jatropbus is so pure that it will run a diesel tractor without refining –pressing and filtering are all that’s needed. Among the bona fide trees – providing more valuable oils – are the candlenut tree, Aleuritis moluccana, and the tung tree, A. fordii, and the Chinese tallow tree, Sapium sebiferum. Most important of all, however, by far, is the rubber tree, Hevea brasiliensis, a native of Brazil but now grown also in Africa and Asia, and most prodigiously in Malaysia. (Note, though, that the archetypal house plant known as the ‘rubber plant’ is a species of Ficus or fig.)
Rubber in its raw form is latex, a creamy gum that plants exude when wounded. Why they do this is a mystery: none of the many explanations (most obviously, that latex is intended to heal the wound) seems to stand up to scrutiny. But a great many plants do it, from quite a few families. Several have been tried out as a source of rubber. The Russians have produced rubber from their native Guayale. Even dandelions produce latex. Notoriously, in the late nineteenth and early twentieth centuries, the Belgians enslaved many thousands of Congolese people and sent them off into the jungle to tap latex from the vine Landolphia (a relative of the periwinkles in the family Apocynaceae). The endeavour produced some 60,000 tonnes of rubber, at an estimated cost of one human life for every 4 kilograms.
But Hevea is the best source by far. Various species are widespread through the American tropics, a few trees per hectare, living in the wild for a hundred years or so and growing to 40 metres. The native people had known their properties for centuries, and made play-balls and religious figures from their latex. Europeans came across them and the people who made use of them in the eighteenth century. In England, the chemist and theologian Joseph Priestley found that balls of latex would erase pencil marks, and so coined the deprecatory term ‘rubber’. Many other languages prefer more dignified variations on the beautiful native word cachuchu: ‘weeping wood’.
Rubber first took off commercially in the mid nineteenth century, with new technologies to extend its use. First technologists learned to shape it. Then in 1839 (patented in 1844) the American Charles Goodyear developed ‘vulcanization’: hardening the rubber by combining it with sulphur. Rubber made an enormous impression at Prince Albert’s Great Exhibition in London in 1851: Goodyear built an entire ‘Vulcanized Court’, with rubber walls, ceiling and furniture. The turnaround came with John Dunlop’s invention of the rubber tyre in 1888. The rise of the motor car from the late nineteenth century onwards, and particularly Henry Ford’s mass production, were the final flourishes.
For a time, Brazil did very well out of rubber. Indeed it seemed set to transform the country’s economy. The focus and symbol of the trade was and is Manaus: a teeming city built a thousand miles up the Amazon. In truth this is not quite so bizarre as it might seem since the Amazon is broad and access is easy (relatively speaking), and once the trees had been cleared around the place where Manaus now stands, the ground proved solid enough. (New York was once a forest too, and London was largely swamp. Venice, in effect, still is.) Manaus blossomed in the early decades of the twentieth century when Henry Ford was turning out the first true ‘people’s cars’ in the form of the Model T. In a fit of what seemed at the time to be perfectly justified bravado, Manaus built itself an opera house, and very splendid it still is. Caruso sang there and Pavlova was due to dance but could not face the final leg of the journey and sent her apologies from Belém, at the mouth of the Amazon. Whether the megastars who favoured Manaus with their glittering presence were aware of the horrendous cruelties inherent in old-style rubber production (torture, rape, enslavement and murder), I have no idea.
But the seeds of destruction had already been sown, literally, before Manaus was even built. In the 1860s Sir Clement Markham of Britain’s India Office, who had already organized the introduction of Cinchona (for quinine) from tropical America to plantations in India, sought to do the same with Hevea. Botanists from Kew soon established that Hevea brasiliensis was the best of the genus. Eventually, in March 1876, Henry Wickham brought 70,000 seeds of Hevea brasiliensis from Brazil to Kew, where just over 2,000 of them germinated. From Kew young plants were sent to Ceylon (now Sri Lanka) and Malaya (now Malaysia). Soon the Asian plantations were the world’s major producers. Their only real setback since then has come from the rise of synthetic rubbers, first developed in America during the Second World War when the Japanese occupied the principal rubber plantations of the East: the US synthetic rubber programme was second only to that of the atomic bomb. By the 1980s, natural rubber filled only 30 per cent of the world market but by 2002 it had sprung back to 40 per cent. Perhaps this is part of a general world shift from industrial chemistry to biotechnology. But natural rubber still fills various special niches, for example in aeroplane tyres and in condoms.
Brazil now produces far less rubber than Malaysia: for one thing, its plantations are beleaguered by an untreatable fungus called South American leaf blight, which those of Asia have escaped. But for Brazilians, rubber is still of immense cultural importance. The rubber tappers’ movement in Acre in the 1980s did much to draw the attention of the West to the plight of the Amazonian forest. Overall, the Brazilians continue to smart at what they see as the theft of their inheritance. Some argue that Henry Wickham did nothing underhand. At least, he declared his cargo to the Brazilian customs officers as ‘exceedingly delicate botanical specimens specially designate for Her Majesty’s own Royal Gardens at Kew’: disingenuous to be sure, but not inaccurate. Others see the entire episode as biopiracy. All in all it does seem most unjust, but this is a tricky area. After all, the Brazilians are doing very well out of eucalyptus, which Europeans brought from Australia in 1828 (though it has not always been planted wisely and in places is a serious pest). Brazil is also pushing ahead vigorously with teak, from India. Its biggest agricultural export these days is soya – a Chinese plant. Brazil’s cattle came originally from Europe (and to some extent from India). For their part, the Chinese grow enormous quantities of potatoes and maize, which are American, and wheat, from the Middle East. Deciding who has a right to what is a key issue of present-day politics and globalized commerce. (More in Chapter 12.)
On more practical matters: plantation rubber trees generally start producing useful amounts of latex at around seven years; are producing maximally by age fifteen; and are generally chopped down and replanted after thirty years (when they are about 20 metres tall). So the grower has about twenty-three productive years out of thirty. In the past the timber was simply burned, but it is a pleasing reddish brown, and strong, and in recent decades has become a major crop. Malaysia and Thailand now export nearly $1.5 billion worth of rubberwood furniture. South-East Asia could harvest more than 6.5 million cubic metres of rubberwood per year – almost as much as the entire timber harvest of Central America.
In Malaysia I found the rubber plantations in many ways attractive: green and aromatic shade in a colonnade of trunks, and all as cool as Sussex. But the work – slashing the bark every day and replacing the receptive cups – is desperately tedious, and recruitment of labour is difficult. My solution would be to make the work more
interesting –by integrating smaller plantations with mixed farming, as I have seen in China. Indeed, rubber trees do lend themselves to agroforestry. Other crops (including valuable herbs) may be grown among them and their shade is good for livestock. As a bonus, they produce big oily seeds – which are thrown spectacularly for several metres as the fruit dries and splits. In the wild, in Amazonia, these seeds are dispersed by large river fish. In plantations, I would have thought they would be ideal for turkeys. I would hate to be a traditional rubber-tapper, and feel sorry for those who are (and their daughters in Malaysia take off for the electronics factories). But a mixed exercise in agroforestry, with other crops and livestock, is a different proposition all together. A grand challenge: most interesting.
Then there are the Rhizophoraceae – the family of Rhizophora, the red mangrove trees. Mangrove forests grow at the edge of the sea throughout the tropics: in northern Australia, South-East Asia, West Africa, around the Red Sea, along the north coast of South America, on both coasts of Central America and in the Caribbean. Although mangroves occupy only 180,000 or so square kilometres of the earth’s surface they are hugely important ecologically and economically. Around their roots breed a host of sea creatures, including many ocean fish. Local people take as much from the mangrove forest as forest people take everywhere – fuel, timber, fruits – and fish, too. Offshore from the mangroves, typically, are the seagrasses – food for fish, molluscs, manatees and marine iguanas – and beyond them lies coral reef, which in diversity of wildlife is second only to tropical forest. The mangroves, if left intact, protect the seagrasses and the reefs. Since the mangroves, seagrasses and corals are all nurseries for marine creatures, the consequences of mangrove destruction extend through all the oceans. Yet they are being destroyed – to make way for marinas and promenades, for lagoons to raise tropical shrimp for Western supermarkets, or even, it sometimes seems, just for the sake of it. In Panama in 2003 I was shown a mangrove that had been filled in with rubble to provide a park for containers, of the kind used for ocean-going cargo ships. The local government bought the idea from some entrepreneur on the grounds that it would provide employment. The only employee when I was there was a man with a gun, to keep people off. The entrepreneur, having pocketed the taxpayers’ money and destroyed the mangrove forest (and the wild creatures, and the livelihoods of the people who were living there) was about to sell his barren dump to the Chinese. That’s business, apparently.
To return to the natural and saner world: about eighty species of trees have mastered the adaptations needed to live in the intertidal zone. Of these, thirty or forty are core species, which turn up in most mangrove forests; and of these the most important overall are seven or eight species of Rhizophora.
The third great arborescent family of Malpighiales is the Salicaceae. It is named for the genus Salix, the willows. There are about 400 species – although as outlined in Chapter 1, they are hard to identify and very prone to hybridize, so it will always be effectively impossible to say exactly how many there really are. They range from small shrubs to big trees, and from the tropics to the extreme north. Up cold and windy mountains, and on the edge of glaciers up towards the Arctic, they are often the chief of the woody species. In such territory, they send out underground stems to form vast clones: a wood that in effect is a single plant. Thus the creeping willow, S. repens, colonizes marshland and begins its transition into forest. Most willows like the edges of rivers, where they are commonly planted to stabilize the banks. They may serve, as reedbeds do, to purify the water. Some are ornamental: the original weeping willow in particular, S. babylonica, originated in China, drooping languidly over lakes and lazy rivers as if specifically intended for patterned tea sets.
Willows belong in the northern hemisphere, although one (S. mucronata) crosses the equator in Kenya. Many kinds live in western China, which is truly one of the world’s great centres of diversity; but, like so many trees, these Chinese willows have not yet been properly studied. Willows are nearly all dioecious (males and females on separate plants) and produce catkins that are usually pollinated by insects, although wind probably plays a part. Their seeds are tufted, and float on the wind. The different forms of willow find many traditional uses: the thinner twigs (especially of osiers, S. viminalis) for baskets, coracles and hurdles; the bigger timbers for construction. Female clones of S. alba var. caerulea are the sole source of wood for cricket bats (though sadly threatened from time to time by the bacterium Erwinia salicis). The finished cricket bat is a botanical extravaganza: white willow for the blade, bamboo and rubber for the handle, plus twine to bind the handle and glue to hold it in the blade, both of which may come from plants, and linseed to keep the bat supple. Willow is also an important fuel wood, now much vaunted as a source of biomass to supply energy without exacerbating global warming. Finally, the bark of willow is particularly rich in salicin, the root molecule of salicylic acid, the stuff of aspirin; of proven use as an analgesic and anti-inflammatory, and now favoured to reduce blood clotting and guard against thrombosis.
Also in the Salicaceae and closely related to willow is poplar (Populus), the twenty-nine or so species of which include the aspens, like North America’s quaking aspen, P. tremuloides. Poplars are hugely favoured for plantations worldwide, for matchsticks and paper pulp. They also serve as windbreaks and (like eucalypts) help to dry out wetlands, acting as they do like wicks. A major task now is to conserve their genetic diversity, as the wet river banks that they favour are drained and contained. The levees of the Mississippi have hugely reduced the natural regeneration of the native P. deltoides. Attempts are afoot worldwide to conserve the diversity in arboretums. In Europe, EUGORGEN, the European Forest Genetic Resources Programme, is intended to conserve the natural diversity of the black poplar, P. nigra, and holds nearly 2,800 clones from nineteen countries. In the Pacific north-west, GreenWood Resources holds 100 stands of P. trichocarpa, to counteract the losses along the Columbia and Willamette rivers and their tributaries. Efforts to conserve poplars in situ include the Tarim River nature reserve in the Xinziang Autonomous Region of China, largely intended to conserve the remaining third or so of the original P. euphratica; and a plan supported by the International Poplar Commission and the United Nations to conserve the native variety of P. ciliata in the Himalayan foothills of India. Such efforts are heartening. Populus, however, is only one among many thousands of genera of trees, and the vast majority are receiving no help at all. Even if they escape extinction, few will escape severe genetic diminishment.
There are some other notable Salicaceae too – including some that are traditionally placed in the Flacourtiaceae, which Judd enfolds within the Salicaceae. Among them are the Maracaibo boxwood, Gossypiospermum praecox, from Cuba, the Dominican Republic, Colombia and Venezuela – highly favoured for specialist tasks, not least for the working parts of pianos; and odoko from West Africa, species of Scotellia, hard and tough and excellent for floors.
Several other families in the Malpighiales are worth a passing mention. The Violaceae in temperate regions manifest as herbs including violets; but in the tropics produce some fairly mighty trees. The Malpighiaceae, for whom the order is named, include the Barbados cherry. The Clusiaceae are best known as the family of St John’s wort, which finds favour as an antidepressant. But it also includes some handy trees – not the least being the 200 or so species of Garcinia which include the mangosteen, G. mangostana, a native of Malaysia with fruits the size of a ping-pong ball, whose brownish purple leathery skins enclose treacly and truly delicious (I can vouch) creamy-white segments. An excellent fruit, though the trees are slow-growing and not easy to cultivate.
The Ochnaceae family includes the ekki tree from West Africa, Lophira alata, from whose timber (for some reason) the tracks of the Paris metro are made. The metro trains have rubber tyres. I venture that few who ride the Paris metro realize their debt to the trees of the Malpighiales.
Star fruit and Coachwood: ORDER OXALIDALES
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nbsp; The Oxalidales is yet another order that has been subject to serious reclassification. The family for which the order is named, the Oxalidaceae, is primarily tropical and subtropical and is known to northerners primarily through wood sorrel (Oxalis acetosella). It does include a few small trees, however – one of which is the star fruit or carambola, Averrhoa carambola. The fruit is juicy, sometimes sweet and sometimes acid, is deeply ribbed and thus star-shaped in cross section, and has lately become fashionable outside its native Indonesia. Modern DNA studies also place the Cunoniaceae within the Oxalidales: and these include Ceratopetalum apetalem, a tall (18–24 metre) and valuable timber tree from New South Wales, known as coachwood (or lightwood or scented satinwood). Its browny-pink, fragrant timber is used for lots of things, especially joinery and mouldings, but also for gunstocks, shoe-heels and musical instruments. Thus the wood sorrel emerges as yet another homely herb with wildly exotic relatives.
Trees for Fodder, Fuel, Flowers and Beautiful Timbers: ORDER FABALES
Within the Fabales order are four families but the only one that need delay us is the Fabaceae – and they should delay us plenty because, together with the grass family, Poaceae, the Fabaceae is the most important plant family of all, both ecologically and economically. It is also the third largest with 18,860 or so known species in 630 genera, but the inventory is still rising fast. Only the orchids and daisies have more species. Fabaceae used to be called Leguminosae – the pods are called ‘legumes’. The old family name is now officially defunct but the adjective ‘leguminous’ and the informal noun ‘legume’ (applied to the whole plant as well as to the pods) live on.
Fabaceae take every form: herbs such as vetches, clovers and alfalfa; vines like peas and runner beans, which climb by twining and/or with tendrils; woody climbers like Wisteria; shrubs like gorse and broom. But in addition, many of the tropical genera in particular make fine trees that are of huge significance worldwide in forests and savannah, while providing every kind of service for humanity and our domestic animals.
