by Colin Tudge
In its new form, then—subsuming the Tiliaceae, Sterculiaceae, and Bombacaceae—the Malvaceae emerges as a truly remarkable family of truly remarkable trees. But the Malvales order also includes another arboreal family that is clearly discrete from the Malvaceae: the Dipterocarpaceae.
The dipterocarps are hugely various: 680 or so species in 16 or 17 genera (different taxonomists split them slightly differently). The principal genera are Shorea (by far the most important), Dipterocarpus, and Dryobalanops. Mostly the dipterocarps come from southern or Southeast Asia—Malaysia is the focus, with 465 species in 14 genera—but there are also 49 species in three genera in Africa, and one each in South America and the Seychelles. Between them the different types grow from coast to uplands in many (tropical) climates and in soil both fertile or—often—extremely infertile. Some grow on dry land, but on the whole they prefer the wet: there are many kinds in swamps, and the biggest grow where there is year-round moisture. I am told there is an old plantation of dipterocarps outside Kuala Lumpur, where many individuals exceed 60 meters.
Dipterocarp means “two-winged fruit”—and, indeed, they have fruits roughly like sycamore keys, though often much larger, and sometimes brightly colored. People make wide use of dipterocarps. The fruits of many Shorea and some Dryobalanops are boiled as vegetables. The seeds of both Shorea and Pachycarpae are extremely rich in fat—up to 70 percent—which is similar to cocoa butter though harder, and is much favored for chocolate and cosmetics. (And note again the loose phylogenetic relationship between the dipterocarps and the cacao tree, in the Sterculiaceae. Biochemistry runs in dynasties.) Most dipterocarps also produce useful resins; and a form of camphor comes from Dryobalanops, used as incense.
But above all, the dipterocarps dominate the international market in tropical timber. Shorea species from Southeast Asia are marketed as “meranti.” Various kinds are sold as light red or dark red meranti—red indeed and finely figured, and used for all purposes. Another group of Shorea feature as white or yellow meranti, also with many uses, from floors to ships, plywood, and veneers. Mersawa and krabak are two more, similar Southeast Asian timbers from the genus Anisoptera. Kapur from Malaysia and Indonesia is the genus Dryobalanops. Altogether, the Dipterocarpaceae are a formidable family—comparable in their part of the world with the oaks and beeches from farther north.
FRANKINCENSE AND MYRRH, ORANGES AND LEMONS, MAPLES, MAHOGANY, AND NEEM: ORDER SAPINDALES
The Sapindales are closely related to the Malvales. As in the Malvales, reclassification is in train, so the traditional list of eleven Sapindales families is now reduced to eight. Six of those families—one of them now much expanded—contain trees that are at least intriguing, if minor (ecologically and economically), and others that are of supreme importance both in the wild and to humanity.
Minor but intriguing is the Simaroubaceae family, 100 species of trees and shrubs in 21 genera from throughout the tropics and subtropics. They are biochemically potent and widely deployed in medicine, especially Quassia from Africa, while Picramnia from the Americas was once exported to Europe to treat erysipelas and venereal disease. The white syringa of Africa, Kirkia acuminata, grows to 18 meters, provides useful timber, and also has swollen roots that store water, which knowledgeable locals tap in times of drought. Best known in the gardens and streets of the West is the tree of heaven, Ailanthus altissima. It was first imported to England from its native China in the mid-eighteenth century and thence to the rest of the West. It resists pollution, can grow to 30 meters in less than twenty years, and has compound feathery leaves like an ash, although each may be nearly a meter long.
Minor, too, by world standards is the Burseraceae family—but extremely intriguing, as the family of both frankincense and myrrh. In all there are about 500 species, in 17 genera, throughout the tropics but mainly in Malaysia, tropical America, and Africa, and many provide resins and aromatic oils for perfumes, soaps, paints, varnish, and incense. Frankincense comes from Boswellia carteri, of Somaliland; myrrh is from various Commiphora species, notably C. abyssynica, which grow and are now cultivated in Arabia and Ethiopia. The gifts of the Magi to the infant Christ in Bethlehem were exotic indeed. The first known government-sponsored plant-collecting expedition was in search of myrrh: reliefs on the Temple of Deir el Bahari at Karnak show myrrh trees being transported from the Land of Punt, around 1495 B.C. The Burseraceae family also provides some useful timbers, widely used in Malaysia and Africa. Outstanding is gaboon of Africa, Aucoumea klaineana, used for everything from cigar boxes to sports gear and high-class furniture. Sometimes gaboon is mottled and striped, and then it is highly valued for veneers.
The Rutaceae family is named after the rue, Ruta graveolens, a small aromatic shrub, toxic but also medicinal, and grown in herbal gardens for centuries. It pops up here and there in the plays of Shakespeare, who surely was a competent naturalist, while his son-in-law was an outstanding apothecary. But the Rutaceae overall include about 900 species in 150 genera that grow throughout all the warmer reaches of all continents, including Australasia. By far the best known and important is the genus Citrus: C. limon, the lemon; C. medica, the citron; C. aurantium, the sour Seville orange—a variety of which is also the source of bergamot, the stuff of Earl Grey tea; C. sinensis, the ordinary, sweet orange; C. reticulata, different varieties of which are mandarins, satsumas, and tangerines; C. aurantifolia, the lime (not of course to be confused with Tilia); and C. paradisa, the grapefruit. Closely related to Citrus is Fortunella, the genus of the kumquat, which sometimes turns up pickled on smart dinner tables, though not in my opinion to very obvious advantage.
The Rutaceae also provide some valuable timbers. Various species of Flindersia feature as the cinnamon-colored “Queensland maple”—again for prestige furniture, gunstocks, oars, and what you will. Southern silver ash from eastern Australia, F. schottiana, is just as versatile but pale yellow. From South America comes pau marfin, Balfourodendron riedelianum: tough, pale, flexible; wonderful for oars, tool handles, shoe lasts, furniture, marquetry. Ceylon satinwood, Chloroxylon swietenia, from the southern Indian subcontinent, is called satinwood because it seems to shimmer like folded silk, and is highly prized for panels and veneers. Pale golden West Indian satinwood, Fagara flava, was used widely in the eighteenth century by the great English makers of fireplaces and furniture: Adam, Sheraton, and Hepplewhite.
But satinwoods have largely been ousted from favor by members of the Meliaceae family. The 51 genera (with 550 species) include several outstanding timber trees—indeed, their present and historical importance can hardly be overemphasized. The world star of the families for almost four centuries is the genus Swietenia: the American, or “true,” mahoganies. There are three species—closely related, and often hybridizing in the wild where their ranges overlap. S. humilis, with small leaves, prefers drier country, and spreads north into Mexico. S. mahagoni, the first of the trio to be named (by the Austrian botanist Gerard van Swieten) is from the Caribbean and southern Florida. S. macrophylla, the big-leaf mahogany from Brazil and Honduras, is the giant: an emergent tree, towering above the seasonally dry rain-forest canopy at about 70 meters, with huge buttress roots to reinforce a trunk that can be 3.5 meters in diameter.
Or this, at least, was the pristine state. There is little or no forest left where S. mahagoni and S. humilis once lived. The big-leaf mahogany is still to be found in the forests of southern Amazonia—anywhere between one big tree in every twenty-five acres to three trees per twenty-five acres—and might still, some say, be harvested sustainably and profitably from the wild. It is difficult to increase the proportion in the wild because mahoganies are light lovers and need open ground or clearings to get going. If they are simply planted among other trees they fail. But big-leaf mahogany and S. mahagoni are now widely grown in plantations, particularly in tropical Asia and Oceania, and increasingly in their homelands in the American tropics. Yet they have suffered enormously in plantations from an insect pest, the mahogany shoot borer,
a species of Hypsipyla, which bores into the shoots and turns what should be a straight, proud tree into a mean shrub. The pest can be controlled; but largely because it is perceived as a problem, the world’s plantations of mahogany are only one-twentieth those of teak. Wild mahogany is now listed by CITES, and trade in general is more and more regulated. But it will be interesting to see what happens to mahogany, wild and cultivated, over the next few centuries.
Several close relatives of true mahogany are also fine timber trees: pride of India, Melia azedarach; African walnut, Lovoa trichilioides; South American cedar, species of Cedrela; Asian-Pacific red cedars, species of Toona; the sapele, Entandrophragma cylindricum; and other species of Entandrophragma and of Khaya, which are sometimes called “African mahogany.” Several trees that have nothing to do with the Meliaceae at all are also sold as “mahogany,” including several dipterocarps (of the genus Shorea) and the occasional eucalypt.
Less closely related to Swietenia, yet still within the Meliaceae, is the wondrous neem tree, Azadirachta indica, which featured earlier as the antidote to noxious tamarind. The neem grows to 20 meters or more, with evergreen, roughly ash-like leaves, much valued for their year-round shade. It is native to southern Asia, but its deep roots enable it to thrive in dry, poor soil. It has been planted and become naturalized throughout all tropical Asia, while the British took it to Africa in the early twentieth century to slow the spread of the Sahara. It has also been taken to Fiji, Mauritius, Saudi Arabia, and all tropical and subtropical America, including Florida, Arizona, and California. In the United States there are neem plantations.
There are many outstanding chemists among plants, but the neem is among the greatest of all. For centuries, indeed for thousands of years, the Indians have treasured the neem for medicines: it features in some of the most ancient Hindu texts. Many Hindus begin the new year by chewing neem leaves. Many clean their teeth with neem twigs. They treat skin disorders with its juice, and drink infusions as a tonic. Gum from the bark is used for dye. Neem has also proved active against more than two hundred species of insects, preventing them from feeding and inhibiting their reproduction—discouraging egg laying and disrupting the development of any eggs that are laid. As if to make the point, in 1959 a plague of locusts in India destroyed just about everything that grew, except the neems. The timber is termite-proof, and perfect therefore for hot climates, for everything from furniture to tool handles. Indians put the leaves in cupboards, to safeguard the contents. The leaves also make good fodder, while the seeds are 45 percent oil and provide excellent seedcake for livestock, or oil for lamps. Very properly, the neem is venerated. Many Indian place-names incorporate its name: Neemuch, Neemrana, Nemawar, and hundreds more. The neem is said to have been blessed with nectar, sent from heaven.
Science has reinforced the folk law. Different parts of the neem, but particularly the seeds, contain a host of potent organic compounds shown to be active against just about everything pestilential: bacteria, fungi, viruses, nematodes and mites, as well as insects. A powerful spermicide is in there too, raising hopes in some circles of an effective male contraceptive. Yet the extracts do not seem to harm mammals (including people) or birds. Outstanding among the compounds studied so far is azadirachtin. It is now being incorporated into commercial pesticides not only because it seems innately effective but also as part of a general swing away from industrial chemistry to biotech, based on natural processes and materials.
At this point, the story becomes less pleasant. In the 1990s U.S.-based companies began patenting various components of the neem, which the many excellent scientists of India had not bothered to do because, under Indian law, such medicinal, natural materials are not subject to patent. Thus the beneficent, sacred neem, rooted deep in Indian soil and Indian culture, has become the subject of squalid legalistic wrangling.
The Anacardiaceae are a wonderfully distinguished family. Its 70 genera (with 600 species) include some of the finest ornamentals like sumac, Rhus, and the smoke tree, Cotinus, with its round leaves and wispy gray inflorescences. But these tend to be shrubs rather than trees. The pistachio, Pistacia vera, is a bona fide tree, however, up to about 10 meters. It is native to the Near East and central Asia but has long been cultivated in the Mediterranean and the southern United States for the delectable green kernels of its nuts, eaten as savories and marvelous in ice cream and its Indian equivalent, kulfi. The cashew tree, Anacardium occidentale, is native to tropical America but is now grown widely in India and East Africa—a very useful crop on land somewhat drier than most fruit and nut trees prefer. Cashews are, of course, delectable and also nutritionally potent: 45 percent fat and 20 percent protein. They are commonly served as nibbles before a meal but, in truth, like peanuts, are as rich as any dinner is liable to be. Trees that disperse their seeds with the help of animals must in general attract the animals’ attention, and none does so more promiscuously than the cashew. For the nut itself is presented at the tip of a cashew “apple,” which is more like a yellowish-reddish pear. The effect is of a sculpture on a plinth, though held upside down on the twig. Some people ferment the “apples” to make kaju, a strong liquor. The shells of the cashew contain an oil that irritates the hands but is also used in industry. I encountered my first cashew tree in Pakistan, and although the trip as a whole was memorable, connoisseurs of trees will understand when I say that this was among its highlights.
But the Anacardiaceae offers yet more tropical delights: the mango, Mangifera indica. The mango originated somewhere in India or Burma but thrives in all kinds of soil and is now grown throughout the tropics and into Egypt and Florida, often as a street tree (as in large areas of Belém, although you might think Brazil had enough trees of its own), its dark green, shiny, willow-like leaves providing admirable shade. Often, indeed, mangoes grow virtually as weeds: I have stood beneath a bus shelter in Panama in a storm while mangoes thudded on the roof, and very acceptable they proved to be. They also provide energy (10 to 20 percent sugar) and are particularly rich in vitamin A. Nowadays vitamin A deficiency is a huge issue. Forty million children are believed to be affected, and many are blinded by it (it leads to the drying of the cornea known as “xerophthalmia”). Modern biotech companies are using genetic engineering to produce “golden rice,” that contains some vitamin A, and are claiming thereby to be socially responsible, not to say heroic. But all dark green leaves are rich in vitamin A, and all that’s really needed is horticulture—which was always a part of traditional farming; and with a few mangoes or papayas around, the problem is solved. If high-tech vitamin A–rich rice is ever of help at all, it is only in regions where traditional agriculture has been shoved aside by high-tech, industrialized, monocultural farming.
Finally, completing this lightning sketch of the Sapindales order, and also the rosid eudicots as a whole, comes the extremely distinguished Sapindaceae family. Like the Malvaceae discussed above (and the Cupressaceae, in Chapter 5), the Sapindaceae family is interesting in its traditional form but has become even more interesting of late as other plants, including many fine trees, have been included within it. Thus the Sapindaceae family as now described by Judd embraces the old-style Aceraceae (maples) and the erstwhile Hippocastanaceae (horse chestnuts). In the following, in the interests of clarity and of continuity with most extant texts, I will discuss the three traditional families separately. But in the decades to come, I imagine they will all be discussed as Sapindaceae.
The traditional Sapindaceae family is distinguished enough. It includes about 2,000 species in 150 genera—mostly trees or shrubs but also about 300 vines (which are of the kind that climb by tendrils and are often of huge ecological significance). The family is tropical and subtropical, occurring through the tropical Americas, sub-Saharan Africa, India and eastern Asia, Malaysia and Indonesia, and down into Australia. The family takes its name from Sapindus, which provides oil for soap. It includes some fine fruit trees. The sweet-acid lychee, Litchi chinensis, is from southern China. Botanically t
he fruit is an aril, like that of yew. A close relative is Melicocca bijuga, grown in America. The rambutan, Nephelium lappaceum, is like a lychee with mad hair. Blighia sapida, named after the unfortunate Captain Bligh of the ill-fated Bounty (who in truth was a distinguished amateur botanist and no mean artist), is known in Africa as the akye, and in the West Indies as the akee. It is the national fruit of Jamaica. Akee is again an aril; it tastes like scrambled eggs when cooked, but is poisonous if plucked at the wrong stage. The Sapindaceae family provides some fine ornamentals, too, like Koelreuteria (a street tree) and Xanthoceras (grown for its flowers). The taun tree, Pometia pinnata, from the South Pacific, is magnificent at up to 45 meters, with a trunk up to a meter in diameter and a lovely, smooth, reddish fine-grained timber valued for everything from joists and rafters to pianos and the bars of ships’ capstans.
The Aceraceae, the old-style maple family, includes at least a hundred species in the genus Acer, plus two in Dipteronia. Maples live all over the northern continents, with a huge representation in China and one species in North Africa. This is the field maple, Acer campestre, which is also native to the British Isles and is Britain’s only maple. China has scores of native species. Japan has nineteen. North America has about a dozen. Most maples are small to medium-sized but some are large and evergreen, including a few through Malaysia and into Java. As with oaks, we see that in any one genus some species may be evergreen and some not. Maples are easily recognized for their fruits: paired keys, which spin helicopter-style in the wind, elegantly known in botanical circles as “samaras.” In Dipteronia, by contrast, the seeds sit in the center of a round wing like a yolk in a fried egg. Many maple species produce fine timber, including A. pseudoplanatus, which the British call sycamore and the Americans call planetree maple. Sycamores in Britain are often magnificent but are commonly perceived as invasive weeds. They are despised in part because they do not support such a wide variety of native insects and other animals as oaks do, for example. But they do support an enormous biomass of insects, which in turn support birds. The British are almost certainly right to despise feral rhododendrons, which really do belong elsewhere, although buzzards like them for nesting. But we should perhaps ease up on the sycamore. Maples are good for other things, too. Sugar maple, A. saccharum, and others are the source of maple syrup, to which it is easy to become addicted. Of the many routes to obesity on offer in the United States, that of crisp bacon, a stack of buckwheat pancakes, and maple syrup is perhaps the most seductive of all.