The Tree (20 page)

S
ANDALWOOD AND THE
M
ISTLETOES
: O
RDER
S
ANTALALES

The Santalales are a strange lot. Many are epiphytes (plants that grow on other plants—usually trees); and different groups have evidently evolved the epiphyte mode independently. Many are parasites or semiparasites at least for part of their lives, not simply hitching a ride on trees but tapping into their stems or roots. In the parasitic kinds, the roots are replaced by penetrating organs known as “haustoria.” But some (including some of the parasites!) are valuable trees—and among them is sandalwood, one of the most treasured of all. Sandalwood shows another common quality of the Santalales: some are exquisitely scented.

The order has proved hard to classify. Many traditional taxonomies recognize four families, although modern work on DNA suggests they should be split into seven—but at least two of those seven (says Judd) probably need regrouping. So while the present classification is a little untidy, the Santalales as a whole seems to be a good grouping, a true clade, which is what really matters.

Two families, the Loranthaceae and the Viscaceae (traditionally often combined into one), are those of the mistletoes. They are green and do their own photosynthesizing, but their haustoria tap into the xylem of the trees on which they grow, typically high on small branches, and because they exert more osmotic pressure than the tree itself they suck out the mineral-rich sap. The mistletoes are quaint. Some of the Loranthaceae have bright flowers and are pollinated by birds. The Viscaceae are the “Christmas mistletoes”: favored as Christmas decorations and charms:
Viscum album
in Europe and
Phoradendron leucarpon
in North America. Christmas mistletoes were sacred to the Druids, symbols of immortality—the obsession of Asterix’s chum and mentor, Getafix; and (so legend has it) provided the spear that killed the Norse god Balder. But they also do immense damage to the trees that they favor—mainly members of the Rosaceae and Tiliaceae families, but others too. They create general water stress and ruin the timber by inducing big knots and causing their hosts to produce masses of twigs known as “witches’-brooms” (though there are other causes of witches’-broom as well, including the bacteria that commonly affect birches).
Arceuthobium
of the western United States is the dwarf mistletoe, a major pest of conifers.

The Misodendraceae family contains just one genus, with about eleven species of shrubs that live as parasites on the trunks and branches of the southern beech,
Nothofagus.
As we will see shortly,
Nothofagus
is a great Gondwanan genus, related to the northern oaks and beeches (although now given its own family), that extends all through Australasia and South America; but the particular parasite that plagues it is confined to southern Chile and Tierra del Fuego. I never cease to be amazed by the number of subplots in nature. To the Chilean
Nothofagus
and the parasites of the Misodendraceae their contest is a huge drama—of which virtually all other species, including most of our own, are completely unaware.

Among the twenty-five genera of the loosely defined tropical family Olacaceae (including the Opiliaceae and Schoepficaceae) are shrubs and climbers. There are also some bona fide trees, including some that are locally valuable.
Scorodocarpus
of Asia smells strongly of garlic (its name means “garlic fruit”) and its timber, though smelly, is very strong and used in heavy construction. Tallow wood or hog plum
(Ximenia americana)
is used as a substitute for sandalwood in South America: its timber is hard and yellowy-pink (and its fruits, laden with prussic acid, are extremely bitter). The African walnut,
Coula edulis,
is another very strong timber for building.

But the family that makes the Santalales order so important in human affairs is the Santalaceae, whose 400 or so species in 35 or so genera include
Santalum album,
the sandalwood tree (from the Hindi
sandal
). Its heartwood is the stuff of incense and is beautiful: smooth, the color of pale sand, cutting like wax, carved throughout Asia into a million artifacts (endlessly intricate boxes, elephants inside other elephants, and so on). Entire trunks are smoothed and used as scented pillars in many an Eastern temple. In Mysore it was a royal tree. Apparently, sandalwood is endemic to Timor and its neighboring islands but was brought to India more than two thousand years ago: there are texts that apparently refer to it in the Pali
Milinda-panha
(150
B.C.
) and the
Mahabharata.
Its small, purple-black fruits are dispersed by birds, who presumably helped it spread throughout India. All in all it is immensely valuable commercially and culturally.

Yet the sandalwood tree is a parasite too: at least when young it taps into the roots of a variety of trees. Among its many favored hosts are the strychnine tree,
Strychnos nux-vomica
(a relative of the buddleia). Another host is the pestilential
Lantana,
a shrub imported into India by the British from South America as an ornamental that now seems to grow along every wayside and in every forest throughout the tropics. Dr. Sas Biswas, of the Forestry Research Institute in Dehra Dun, northern India, tells a charming story of sandalwood trees he once found growing in a dead straight row in the middle of nowhere. Why were they there? Who had planted them so carefully and then abandoned them? No one, is the answer. But in the past there had been a garden; and around the garden was a fence; and along the fence grew the inevitable
Lantana;
and sandalwood had grown as parasites from its roots. Now the garden and the fence are long gone and the
Lantana
with it, but the sandalwood remains. Dr. Biswas is adept at reading the history of landscapes from the trees that are left in it: the ambitions of the people who lived there, and the time and chance that in the end reduced their ambitions to nonsense. But nature is opportunist, and lives on.

Finally, members of this whole order are particular pests of some species of acacia trees and other leguminous trees, of which more later. On the other hand, opportunist foresters seeking to grow sandalwood trees in plantations often use acacias as hosts to start them off. It’s an ill wind.

Big, hollow baobabs may double up as funeral parlors and cafés.

9

From Oaks to Mangoes: The Glorious Inventory of Rose-like Eudicots

F
IFTEEN OF THE
eudicot orders are grouped together to form what might be called a subclass, known informally as the “rosids”: the rose-like eudicots. In truth, most of them are not literally rose-like. What really links them all together is not any obvious feature of their flowers but details of their DNA. Yet it seems to be enough. At least in the present state of knowledge, the rosids do seem to form a coherent group. If future scholars decide that they are not so closely related as it now seems—well, that’s the way science goes. Nothing is ever absolutely certain.

Of the fifteen rosid orders, four do not contain significant trees. The Vitales are vines, including the families of grapes and of Virginia creeper. The Geraniales includes the cranesbills and the pelargoniums, parched and sooty-potted on their suburban windowsills. The Cucurbitales includes the family of the melons, cucumbers, squashes, gherkins, gourds, and pumpkins. They are singularly un-tree-like—and yet the Cucurbitales seems to be closely related to the Fagales, which contains only trees, including some of the mightiest, like the oaks and beeches. The Brassicales includes the family of cabbages and wallflowers. Fine plants all. But the rest of this chapter focuses on the eleven rosid orders that do contain trees—including most of the world’s finest and most valued.

W
ITCH
H
AZELS
, K
ATSURA
,
AND
S
WEET
G
UMS
: O
RDER
S
AXIFRAGALES

The Saxifragales are a difficult group, still being sorted out. One reason they are tricky is that within the rosid subclass are many plants that are clearly somewhat primitive—close to the presumed ancestral state. The Saxifragales may be the most primitive of all (the “sister” group to all the other rosid orders). Plants with lots of primitive features and few truly distinctive features are always hard to classify—and modern studies, based on cladistic analysis of DNA, often differ markedly from more traditional treatments based solely on anatomy.
¹
Judd now includes thirteen families within the Saxifragales, totaling about 2,470 species. Among them are many pleasant and well-known herbs and shrubs, including the families of the saxifrages, the stonecrops and houseleeks, and the peonies.

But there are also a few families with some most interesting trees. The Hamamelidaceae includes about 80 species in 25 genera, of which the most pertinent here is
Hamamelis,
the witch hazels.
Hamamelis virginiana,
from the eastern United States, has hazel-like leaves and yields a lotion widely used as an astringent and for soothing cuts and bruises; and diviners, at least in the United States, favor its twigs for detecting subterranean water. Other species of
Hamamelis,
like the winter-flowering
H. mollis
from China, are fine ornamentals.

The Cercidiphyllaceae has just one species,
Cercidiphyllum japonicum
²
—the much-valued katsura tree from the northern temperate forests of Japan, China, and Korea. The katsura is big—up to 30 meters high, with a trunk up to 1.2 meters in diameter—and sometimes it has several trunks, deeply furrowed and often spirally twisted. The timber of katsura is excellent: not too heavy, straight-grained, lustrous, and much prized for wood carving, delicate moldings, high-class furniture, and veneers. It is also used for pencils and cigar boxes, and to make traditional Japanese shoes.

Finally, the Altingiaceae family includes rasamala
(Altingia excelsa)
from Assam through Southeast Asia, valued both for its heavy timber and for its fragrant gum, used in perfumery; and also
Liquidambar,
which grows both in Asia and North America. Superficially,
Liquidambar
species look like maples. Best known is
Liquidambar styraciflua,
the American sweet gum, which grows from New England through Mexico and into Central America. The trees are often huge—up to 46 meters tall and 1 meter in diameter. Sweet gum heartwood is brownish and pinkish, often darkly streaked, and is sold as “red gum”; its sapwood is creamy white and is sold separately as “sap gum.” Both are favored for furniture and veneers (and also more mundanely for packing cases and pallets). When sweet gum bark is wounded it exudes a vanilla-scented resin known as storax or styrax, which is used in perfumery and also as a medicine (as an expectorant and inhalant, and to treat skin diseases). Like maple,
Liquidambar
is famed for its autumn colors, and several kinds are grown as ornamentals.

C
REOSOTE
B
USHES AND THE
W
OOD OF
L
IFE
: O
RDER
Z
YGOPHYLLALES

The plants of the Zygophyllaceae family, the only one in the order, are herbs, shrubs, and trees with showy flowers pollinated by insects that tend to favor dry and salty places and often predominate in scrub. They are also rich biochemically and so are oily and aromatic, and are favored as medicines. Among them is the creosote bush,
Larrea,
to be found out in semideserts and in gardens as ornamentals. Among them too is the genus
Guaiacum
from the Caribbean and Central and South America: small trees (up to around 9 meters tall and 40 centimeters thick), known collectively as “lignum vitae.”

“Lignum vitae” means “wood of life,” for in the sixteenth century the tree was believed to offer a cure for syphilis. In addition, the timber, sometimes greeny-brown and sometimes almost black, is one of the heaviest of all timbers and enormously strong, with prodigious crushing strength. So it finds favor for sculpting and turning (although it is fearsomely hard on the tools) and, for example, for mallet heads: ideal for croquet. Because the wood is innately oily, too, it is self-lubricating, and so is favored for rollers and wheels in pulleys and various machines—especially for parts that are hard to get at and lubricate. The related American genus
Bulsnia
is also sold as lignum vitae, but is not so good. But
Guaiacum
is becoming rare, and indeed is now covered by CITES (the Convention on International Trade in Endangered Species), which at least provides some legal control over harvesting.

S
PINDLE
T
REES AND
K
HAT
: O
RDER
C
ELASTRALES

The Celastraceae family is named after
Celastrus,
a climber known as bittersweet.
C. scandens
is the native North American species, much admired. But it is now largely replaced by
C. orbiculatus,
introduced from East Asia—an aggressive weed that grows over everything, often smothering other plants, and is pertinent here not as a tree but as a spoiler of trees (at least when out of its native lands).

The 55 genera of Celastraceae also include the genus
Euonymous.
Among these is
Euonymous europaeus,
the spindle tree, whose fine-grained wood is favored for carving and turnery, and whose seeds yield an oil for soap and a yellow dye for coloring butter.
Euonymous hians,
from Japan, is also used in turning, and for making printing blocks. Other species of
Euonymous,
including some that are shrubby rather than arboreal, yield a rubber-like latex; some feature in Native American medicine. The pharmacological propensities of the Celastraceae family are also evident in the khat tree,
Catha edulis,
whose leaves are chewed in the Middle East as a stimulant. The kokoon tree from Sri Lanka
(Kokoona zeylanica)
yields a useful oil.

R
UBBER
T
REES
, M
ANGROVES
, W
ILLOWS
, P
OPLARS
,
AND
S
OME
T
RULY
P
RODIGIOUS
H
ARDWOODS
: O
RDER
M
ALPIGHIALES

The 35 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 goatproof, and much favored 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
Jatrophus
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,
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 houseplant known as the “rubber plant” is a species of
Ficus,
or fig.)

Rubber in its raw form is latex, a creamy gum that certain 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
Guayule.
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 endeavor produced some 60,000 tons of rubber, at an estimated cost of one human life for every four kilograms (about nine pounds).

But
Hevea
is the best source by far. Various species are widespread through the American tropics, several trees per acre, living in the wild for a hundred years or so and growing to 40 meters. 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 called it “rubber,” meaning a thing to rub out mistakes with. The term hardly does justice to one of nature’s most intriguing inventions. 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”: a way of hardening the rubber by combining it with sulfur. 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 tire in 1888. The rise of the motorcar from the late nineteenth century onward and, particularly, Henry Ford’s mass production were the final flourishes.

For a time, Brazil did very well out of rubber. Indeed, rubber 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 favored 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.