by Colin Tudge
Then again, among living angiosperms, two quite opposite kinds of flower have been mooted as the most primitive. One is the big showy kind, as in waterlilies and magnolias. The other is a simple but small and modest kind, as found in pepper vines (the plants that produce peppercorns; not sweet or chilli peppers). But the first ancestor of all the flowering plants either had magnolia-like flowers or pepper-like flowers. It could not have had both. If it had some compromise form, able to evolve either way, then we simply do not know what it was. The same kind of dilemma applies to fruits. Are the most primitive the small and scrutty kinds, or the big and fleshy kinds, packed with seeds, like custard apples?
So the origin of flowering plants remains mysterious, but we do know that they are now immensely various, and their variety is reflected in their taxonomy. Roughly speaking, there seem to be around 300,000 species. Different botanists differ in the way they divide these species into families: recent published papers recognize anywhere between 387 and 589 families. The specialists who form the Angiosperm Phylogeny Group have, for the time being, plumped for 462. Only specialists can get their heads around so many, and so it is useful to group the families into orders. Again, different taxonomists recognize different numbers of orders, but the authorities I am following in this chapter (who I refer to collectively as ‘Judd’) divide them into forty-nine, most of which contain trees. Forty-nine is still too many for most people to bother with, but most of the trees are contained within about thirty of the orders, and that is manageable.
One last word before the catalogue begins – on the idea that was first mooted by John Ray in the seventeenth century, and was developed by Antoine Laurent de Jussieu at the end of the eighteenth. Ray (you will remember from Chapter 2), divided flowering plants into those with narrow leaves and those with broad leaves; and Jussieu found that the narrow-leaved types were ‘monocots’ (with a single cotyledon) while the broadleaved types were ‘dicots’ (with two cotyledons). So the distinction has stood for the better part of 200 years. In rough and ready terms, the distinction still stands. But those interested in phylogeny – the true history of plants – as opposed merely to convenience, must now make a serious modification. For it is clear that the first ever flowering plants were dicots. Some of those early, primitive types are still with us – including the magnolias, the waterlilies and the peppers.
After some time, there arose from among the ranks of the primitives a new group that went off in novel directions. Some of these avantgarde types evolved into the monocots – which thus emerge as comparative latecomers. Some evolved into a quite new kind of dicot, now known collectively as the ‘eudicots’ (‘eu’ meaning ‘good’). The monocots are a true clade – all deriving from a common ancestor. The eudicots are also a true clade. It is also possible, indeed quite likely, that the ancestor of the monocots was also the ancestor of the eudicots – in which case the monocots and the eudicots together form a true clade.
But the primitives (magnolias, peppers, etc.) remain out on their own: not members of either of the two modern clades (although flowering plants as a whole form a true clade).
So in effect we now have three great groups of flowering plants. First there is a mixed bag of ‘primitive dicots’: not a clade; just the kinds that seem to have retained many of the main features of the first ancestor. Then there are the monocots, which are a true clade. Then there are the eudicots – another true clade, this time of derived dicots. The primitives are discussed in the rest of this chapter; the monocots have the next chapter to themselves; and the eudicots are spread over the two chapters after that (because they are too diverse to be accommodated comfortably in one).
The Mixed Bag of Primitive Dicots
As you can see from the chart, the primitive dicots include seven orders. The three extreme outliers need not delay us too long. At least, the Amborellales does include one tree – which, like so much of botanic interest, lives in New Caledonia. It is aromatic, but it is only small. The Nymphaeales is the order of the waterlilies: of huge interest botanically and ecologically, but emphatically non-tree-like. The Australobaileyales are interesting as the possible sister group of all the other flowering plants – and because the order contains the family Illiciaceae, which includes the genus Illicium. From the bark of various species of Illicium, comes the spice star anise.
The remaining four orders collectively form a group that botanists refer to as the ‘magnoliid’ clade. All of them contain trees, and three of them contain some very significant trees indeed.
Magnolias, Custard Apples and Nutmeg: ORDER MAGNOLIALES
The Magnoliales order contains around 2,840 species in six families, of which the three outlined here – Magnoliaceae, Annonaceae and Myristaceae – include highly significant trees.
Some traditional classifications1 list up to twelve genera in the Magnoliaceae. But Judd combines eleven of the traditional types into Magnolia; the other genus is Liriodendron. Between them they include 218 species, and they have the kind of distribution that we have already seen among the conifers: many in South-East Asia, from the Himalayas out to Japan, and many more in the south-eastern United States and Central America, with some in South America. Why are they spread out this way? Did they at some point leap the Pacific? Perhaps. But there are fossil Magnoliaceae in Europe and even in Greenland – which suggests that the family may once have spread more or less continuously from South-East Asia to the Americas before the two continents drifted apart, and that they have simply died out in the middle of their range.
Magnolia is of course magnificent, with some of the most stunning flowers of any tree – sometimes star-like, sometimes huge like water-lilies. Their greatest value for humanity is in horticulture; and I commend to you the magnificent botanic gardens in Yunnan, south-west China, which has a hundred or so species. Some magnolias give serviceable timber. The bark and flower buds of M. officinalis of China are used medicinally, and are a valuable export. (China is also one of the world’s greatest centres of biodiversity and its potential for ecotourism is unsurpassable. It is up there with Africa, Madagascar and Amazonia).
Liriodendron includes the two species of tulip trees – one Chinese (L. chinense) and one North American (L. tulipifera). Their leaves are strange and absolutely characteristic – like glossy, dark green versions of maple leaves, but with the pointed tip cut out. Their flowers are tuliplike, although difficult to appreciate since tulip trees can be big (the tallest in England is 36 metres) and the flowers are born aloft. The American tulip tree yields a creamy timber, with streaks of olive green, black, pinkish brown or even steely blue, from growing in mineral soils, which is much valued for carving, and for doors and suchlike. As a timber tree, Liriodendron is sometimes known as ‘yellow poplar’ and is sold as ‘American whitewood’. Such names do it scant justice.
The 2,300 species of Annonaceae, arranged in 128 genera, form a glorious family widely spread through lowland tropical and subtropical
You can’t mistake the leaves of the tulip tree, Liriodendron
forest. In many ways they seem wonderfully primitive. Their flowers are pollinated by beetles – which they have evolved to encourage: they have a fruity odour, and they reward their visitors with thick fleshy petals for feeding on, and extra fleshy tissue that serves no purpose except to provide beetle food. Some flowers of the genus Annona are able to heat up – a fairly common trick among several plant families. This encourages the beetles to stay inside the flowers overnight and mate, so becoming covered in pollen. Various genera, notably Annona and Rollinia, provide marvellous fruits of the kind that seem primitive and in Cretaceous times doubtless were food for dinosaurs: big and pulpy, with many big seeds. Custard apple (Annona) with its grey, tessellated skin, is the best known of these fruits in the West. Others include the cherimoya, soursop and sweetsop. The fruits of Monodora myristica are sometimes used in place of nutmeg, and some Annonaceae with their thick, fibrous bark are grown as ornamentals, at least in warm countries.
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sp; The third important family of the Magnoliales order is the Myristicaceae. It includes 370 known species in seventeen genera, which occur across the tropics: in South and Central America, across equatorial Africa, through south India and South-East Asia and into Queensland, Australia. The trees are usually dioecious (only one sex per tree) and although their flowers are small and inconspicuous they are pollinated by insects – beetles and thrips. Clearly they are very different from those of the Annonaceae or Magnoliaceae – illustrating that although flowers are one of the main guides to classification, they may nonetheless differ enormously even between closely related families.
The biggest genus is Myristica with 125 species, centred on New Guinea. Myristica fragrans from the Molucca islands of Indonesia is the most economically important of all the family: its big seeds are nutmeg; the fleshy coating of the seed (the ‘aril’) is scarlet while it remains on the tree (although concealed inside a thick fruit with a pale green skin) but is a pale buff-pink after drying, and is the stuff of mace. The seeds of the Brazilian genus Virola are ground to make snuff that is hallucinogenic. (Perhaps the world needs more hallucinogens rather than less. The puritanical attitude of the West might more properly be seen as an offence against nature. More in Chapter 12.) V. surinamensis, whose seeds are waxy, are used to make ‘butter’ for eating and for candles. So too are those of Gymnacranthera farquhariana from India.
Greenheart, Stinkwood and the Green Bay Tree: ORDER LAURALES
The Laurales order includes around 3,400 species in seven families, of which the most significant is the Lauraceae (named, incidentally, by Antoine Laurent de Jussieu, who first made clear the monocot–dicot distinction).
The members of the Lauraceae family are mostly trees or shrubs –in all there are around 2,500 species in fifty genera, a huge presence in tropical wet forests worldwide, and in the subtropics. They serve humanity in many ways: extraordinarily nutritious fruits, many fine timbers, and a host of medicines and other drugs. The Lauraceae illustrate beautifully how biochemistry runs in botanical families.
Best known of all Lauraceae fruits is the avocado, Persea americana, native to Central America. It has more protein than any other fruit, and is 25 per cent fat. It also has a wonderful strategy to prevent inbreeding. As with other Lauraceae, it is pollinated by insects. It has two kinds of flowers, inventively dubbed A and B: some individuals have A flowers and some have B flowers. The stigmas of A flowers are receptive to pollen only on one particular morning, while the anthers of A flowers do not release their pollen until the afternoon of the same day. In B flowers, the stigmas are receptive on one afternoon, while pollen is not released until the following morning. So A flowers can be pollinated only by B flowers, and B flowers can be pollinated only by A flowers.
Many Lauraceae have oil cavities in their leaves and elsewhere, and many are aromatic. Thus the family includes the bay trees (Laurus nobilis), sassafras (Sassafras albidum), cinnamon (Cinnamomum verum) and camphor (C. camphora), once much used in mothballs (though modern mothballs are of naphthalene) – one of many examples of a tree’s own insect repellent turned to human use.
Among the many valuable timber trees in the Lauraceae family is the Queensland ‘walnut’, Endiandra palmerstonii, which grows to a magnificent 40 metres or more and whose timber resembles European walnut (which comes from the quite different Juglandaceae family). It has pinkish sapwood and pale to dark-brown heartwood, streaked with pink or purple-black – much prized for furniture of the boardroom kind. The mangeao of New Zealand’s North Island (Litsea calicaris) is another giant (40 metres or more), giving cream to pale-brown timber that is favoured for everything from turnery to dance-hall floors to pit props – and also for excellent veneers for export. Imbuia (Phoebe porosa) from Brazil is yet another forest giant (up to 40 metres) with a dark-brown, fine-grained, lustrous timber that again is much coveted for high-class joinery.
The many fine trees of the genus Ocotea are prized both for their beautiful timber and for their broader biochemistry. South Africa’s stinkwood (O. bullata) is 18 to 24 metres tall in the forest, yielding a dark timber with a fine grain that is indeed malodorous when freshly worked but settles down when dried. Ocotea usambarensis from Kenya is camphorwood. It is up to 45 metres tall, yields a greenish-brown timber that matures to deep brown, smells of camphor and is much favoured for making wardrobes, effectively with the mothballs built in. (I have found, in travels with tropical loggers, that many trees are surprisingly smelly when first cut, and not always pleasantly so.)
But the most famous of all the Lauraceae timbers comes from the greenheart (O. rodiaei), the pride of Guyana. Again it reaches up to 40 metres, with a long cylindrical trunk that may be 25 metres tall and a metre in diameter. The sapwood is pale yellowy-green, the heartwood light olive to dark brown, often streaked with black. Greenheart again is highly versatile: much favoured in maritime circles for jetties and groynes, and in ships for planking and stern posts, but also for turnery and the butts of billiard cues. It is used to make longbows, too, the technology of which has come on apace since the English first juxtaposed the heartwood and sapwood of yews. Modern longbows are laminated and greenheart often forms the central layer.
In addition, the nut of the greenheart yields material called ‘tipir’ which the native people of Guyana have long employed as a medicine. The Wapishana tribe grate the nuts and use the extract to stop haemorrhages, prevent infections, and as a contraceptive. In the late 1990s, however, an American entrepreneur, after spending time with the Wapishana, tried to patent tipir as an antipyretic useful in preventing flare-ups of malaria, and perhaps for treating cancer and Aids. The tribe accuse him of theft: ‘biopiracy’. The dispute rumbles on. Meanwhile greenheart, precisely because it is wonderful in so many ways, is being seriously overlogged. But still it is outstanding even among the distinguished family of Lauraceae, which are huge players in tropical forests and economies worldwide.
Winter’s Bark and White Cinnamon: ORDER CANELLALES
There are only two families in the Canellales order. The Winteraceae family includes up to 120 species (no one is quite sure) in seven or eight genera, largely from around the coasts of South and Central America, eastern Australia and New Guinea, plus one in Madagascar. Several have peppery leaves and bark that are said to be medicinal: best known is winter’s bark (Drimys winteri), which was once used to prevent scurvy. The wood of the Winteraceae is strange: the conducting tissue of the xylem contains only tracheids – rows of cells with perforated ends – as in a conifer. They do not lose the cell walls at the ends to form the continuous tube-like vessels that are more typical of broadleaves. But it is not clear whether this arrangement is primitive or secondary: the ancestors of the modern Winteraceae may have had vessels, which may subsequently have been lost. As we have seen, evolution often leads to simplification, and several other groups of flowering trees, unrelated to the Winteraceae, have wood with tracheids rather than vessels.
The second family, the Canallaceae, includes sixteen or seventeen species of aromatic trees, in five genera. The bark of Canella winterana is also known as ‘white cinnamon’, and is a tonic and a condiment; it is also used to poison fish in Puerto Rico (so they can be scooped out of the water). The aromatic wood of Cinnamosma fragrans of Madagascar is exported via Zanzibar to Bombay, where it is used in religious ceremonies. The bark of Warburgia ugandensis of Uganda serves as a purgative, while its leaves are used in curries and its resin is handy for mending tools.
Black Peppers, White Peppers and Dutchman’s Pipe: ORDER PIPERALES
The last order of primitive dicots is the Piperales. As defined by Judd it includes five families, of which the most significant is the Piperaceae, mainly of rainforests throughout the tropics. Its 2000 or so species include some small trees but its best known members are the woody vines Piper nigrun, source both of black and white pepper, and P. betle, whose peppery leaves are chewed with various spices and betel nut (the fruits of the palm Areca catechu) to provid
e what the herbal manuals call ‘a mild stimulant’, the red juice of which dribbles down many a beard on the Indian subcontinent (including mine, from time to time).
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From Palms and Screw Pines to Yuccas and Bamboos: The Monocot Trees
An arborescent relative of asparagus: the dragon tree
If some earthly firm of engineers had designed the magnolia or the bay tree, they would be pretty pleased with themselves. Here, they would conclude, is the finished article: root, trunk, branches, leaves, fruits and well-protected seeds; everything taken care of, the whole structure beautifully integrated, beyond improvement; the apotheosis of the plant.