by Colin Tudge
The fruits of palms are immensely variable. Most are ‘drupes’ – a fleshy fruit with a stone, enclosing one or two seeds. Often they are small and berry-like. But often too they are huge, sometimes warty and sometimes fibrous – like the coconut. The seeds of Lodoicea, endemic to the Seychelles, are the biggest of any plant: like a great pair of brown wooden buttocks, and also known as the double coconut, occasionally as the bum seed and more felicitously as coco de mer. Lodoicea seeds are dispersed by water (like those of coconut and nipa palms) and can stay at sea for many months.
Many palm fruits and seeds are rich in fat, including oil and wax. The coconut is a staple in many countries and a source of valuable oil. The oil palm (Elaeis guineensis) from West Africa provides an oil that’s used for many purposes, including soap. Oil palm has long been Malaysia’s second biggest earner after rubber, and is now being grown on a larger and larger scale throughout the tropics in the get-rich-quick manner of modern agribusiness, to the huge detriment of the traditional farming that actually feeds people. Attalea is the American oil palm. Copernicia cerifera provides carnauba wax.
Other palm fruit, rich in sugar, are delectable. Besides acai and date, there is the betel nut (from the betel palm, Areca catechu). The 200 species of Bactris include the peach palms. The pulp of the palmyra fruit yields a pleasant jelly; in India the germinated nuts are eaten as vegetables, and its sap, drawn by cutting through the great bract that envelops the base of the inflorescence, yields a sugar called ‘jaggery’ and is also distilled to make arrack or toddy. The Chilean wine palm (Jubaea chilensis) is the hardiest of the pinnate leaved palms and perhaps the sturdiest of all palms, with a trunk a metre thick. From South America too comes the ivory palm (Phytelephas, literally elephant plant): its big and immensely hard seeds are. ‘vegetable ivory’, once favoured for billiard balls.
The coco de mer is the world’s largest seed and a prodigious mariner
Palms yield many fibres. The coir of coconuts, which wraps around the nut, is immensely valuable for ropes, matting and potting compost. It helps the wild seeds to float, as they set out across the oceans from island to island. But the cultivated types have less fibre and more fleshy nut, and are more inclined to sink. The leaves of many palms are used to make mats or walls. Those of Borassus and of the thatch palms, Thrinax and Coccothrinax, are used for thatching. Raffia (Raphia ruffia) is used for weaving mats and baskets. Rattan (Calamus) is stiffer, and is used to make furniture.
Then there are many ornamentals, raised in botanic gardens almost worldwide (including the west of Scotland, anomalously warmed by the Gulf Stream), and along main streets in rich, warm cities from Florida to the Mediterranean to Melbourne. These include the fishtail palm (Caryota), the European fan palm, the cabbage palm (Sabal) and the queen palm (Syagrus). The ugly-attractive Washingtonia, sometimes known as the petticoat palm, is the California fan palm. There are the hundred different parlour palms (Chamaedorea species),
Royal palms may grow to 30 metres. This is a young one
the needle palm (Raphidophyllum), the foxtail palm (Wodyetia) and the graceful, fan-leaved Livistona, from Australia and Asia. The king palm of Australia (Archonthophoenix alexandrae) is magnificent, with its 20 metre tall trunk. Vast, too, is the Indian talipot (Corypha), with a trunk up to a metre across.
Finally, out on its own, an eccentric even among the bohemian palm family, is the nipa palm (Nypa). Molecular studies suggest that it may be the sister of all other palms – closest to the common ancestor. The most ancient palm fossils known are nipa palms, which lends some support to that notion: they date from the (fairly) early Cretaceous, around 112 million years ago. There are many more from the early Tertiary, around 60 million years ago, not least from the depths of London clay (for London from time to time has been tropical and swampy, and with global warming might soon be again).
But nowadays the nipa palm grows among the mangroves of Asia and the western Pacific, sometimes as the dominant species – with its roots in the sea (or at least in very salty water) and its stems prostrate (meaning not upright) and, unusually among true palms, branching. It holds its feathery leaves vertically. Many palms that may live with their feet in water, including the coconut, the oil palm, and the date palm have loosely spaced cells through the core of their roots that allow air to circulate. But the nipa palm goes one step further. It has large air spaces within its roots which connect with cavities in the base of the floating leaves – rather as the lungs of birds connect with further spaces in their bones. Corner suggests that ‘the rise and fall of tide may with slow strokes pump the air around’ inside the nipa palm. It’s as if it breathes, but using tidal energy – a common trick among mangrove trees. Sometimes entire clusters of nipa palms float away on little islands, perhaps to take root somewhere else, sometimes simply to perish at sea. Sometimes, doubtless, animals ride on these floating islands and populate new continents. The present distribution of animals suggests that such events have taken place many times in the past. Nipa seeds, too, like coconuts and cocos de mer are dispersed by ocean currents. Truly, says Corner, the nipa is ‘the swamp palm par excellence’.
All authorities agree that far more research is needed on palms, but it is not easy. A detail, though an important one, is that botanists rely quite heavily on material kept in herbaria – but it is extremely difficult to store the often enormous leaves and inflorescences of palms. Thus, ubiquitous as they are, the palms remain largely elusive. Yet if humanity were allowed to retain only one family of trees from all the several hundreds, the Arecaceae would surely be on the shortlist.
Pineapples, Sedges and Grasses – Including Bamboos: ORDER POALES
Some of the eighteen families within the Poales order are hugely important to our story. The Bromeliaceae includes fifty-one genera and 1,520 species and is best known for the pineapple. But it does have some tree-like forms (including some relatives of the pineapple) and a great many epiphytes – which again include relatives of the pineapple and also Tillandsia the so-called ‘Spanish moss’, which festoons the trees in the swamps of the southern United States, and is very much part of its scenery and folklore. No movie from the Deep South is complete without it. The Cyperaceae, too, the reeds and sedges, include the paper reed or papyrus (Cyperus papyrus) which, growing along the banks of the Nile, is distinctly tree-like.
But the family that is most germane to our story, and indeed to our entire existence, is the Poaceae, formerly known as the Gramineae – the 650 genera, with nearly 10,000 species, of grasses. Poaceae is the most successful plant family on earth, alone responsible for vast biotopes and ecosystems (thanks to their hidden apical bud). It includes the cereals – just three of which, wheat, rice and maize, provide humanity with half of all our calories and more than half of our protein, while the more fleshy grasses feed most of our cattle and sheep. But also, which is what matters here, the Poaceae include the bamboos, in the subfamily Bambusoideae. Truly they are trees, often prominent and sometimes dominant in tropical forests throughout the world. I have gazed up at them in Chinese forests – and up and up and up: some grow to 40 metres, taller than most tropical forest trees. One of the world’s favourite animals, the panda, has turned itself from a perfectly good carnivore (pandas are basically bears) into a dedicated scoffer of bamboo. (Though if you want to catch a panda, lure it into a (bamboo) cage with roast pork. It’s the same with all vegetarians.) Bamboos, like palms, are in many ways eccentric: for example, many flower only at extremely long intervals – every ten to eighty years – and when they do, they all flower simultaneously. How do they manage this? Are they responding to some quirk of light or climate, or to some cryptic message passed between them? And what prompts the message? Some species die after reproducing, sometimes leaving the creatures that depend upon them stranded (like the giant pandas). Binge flowering produces a boom population of young plants over the following years. Many other trees (and animals, such as wildebeest and zebras) practise the same tactic: they produce so m
any offspring, all at once, that their predators cannot possibly catch them all. A steadier output would produce a steady kill. Perhaps, too, the sudden demise of the adult bamboo plants before the next generation gets going helps to reduce the population of pandas.
Bamboos too may compete in the forest as canopy trees
For the traditional peoples of Asia, bamboos are among their greatest assets. They lend themselves to every purpose, from brushes and pens to food, pots, cutlery, furniture and musical instruments of all kinds – percussion, wind and strings. They have created an entire aesthetic of painting and architecture – the swishy calligraphy, the great sagging roofs of palaces and temples. Virtually the whole interior of the headquarters of the International Network for Bamboo and Rattan in Beijing is made from, or veneered with, bamboo. Whole books are devoted to bamboos. They deserve them.
Bananas and the Traveller’s Palm: ORDER ZINGIBERALES
The Zingiberales order is named for the family Zingiberaceae, which includes ginger, cardamom and turmeric – beautiful, wonderful, and valuable, but not trees. But two of the other seven families in the order certainly do include trees. The Musaceae are the bananas. They are giant herbs, rather than true trees, for their stems are not woody, but fleshy and fibrous. But their stalks are thick and tough enough to give them the form of a tree, and they live like trees. The banana genus, Musa, with thirty to forty species, originates in Asia, particularly in Myanmar and New Guinea: Heywood says ‘they are essentially jungle weeds of disturbed habitats’. Bananas are now grown worldwide, and they grow as wayside weeds throughout the tropics. The cultivated banana originated as a hybrid of two species, M. acuminata and M. balbisiana. Extraordinarily, the modern cultivars are triploid –meaning they have three sets of chromosomes, which also means that they are sexually sterile (since the parent cells from which gametes are produced must contain an even number of chromosome sets). So the fruits of the cultivated types are seedless and sterile – all form and no reproductive substance. Thus a bunch of bananas emerges botanically as an infructescence of monocot triploid parthenocarps (and you never know when such knowledge might come in useful). Growers reproduce the plant itself by cloning from suckers. Other species of Musa provide ‘Manila hemp’, for ropes. Africa has its corresponding genus, Ensete, with six species. The exotically decorative Heliconia also belong to the Musaceae.
The Strelitziaceae are exotic and alluring: they include the bird-of-paradise flower, Strelitzia reginae, which is not a tree, and also the traveller’s palm, Ravenala, of Madagascar, which very definitely is. This is an extraordinary-looking plant, again beloved of botanic gardens, with its near half-circle of ragged, banana-like leaves, all springing from the top of a long straight trunk that may be 30 metres high. The flowers, encased in tough bracts, produce an abundance of nectar – which attracts the black-and-white ruffed lemur, to whom the prodigious trunk presents no obstacle at all. As the lemurs feed on the nectar they are coated with pollen. Here we see lemur qua hummingbird, bee or butterfly: the key pollinator.
That ends our rapid recce of the monocot trees. The remaining families of broadleaves all belong to the clade of the modern dicots – known as the eudicots.
Known as ‘traveller’s palm’ – but Ravenala is related to ginger
8
Thoroughly Modern Broadleaves
Trees? Why not? Big cacti form veritable desert forests
Just to recap: Flowering plants (angiosperms) are traditionally divided into two great groups – the dicots and the monocots. The trees among the dicots are commonly known as ‘broadleaves’, to distinguish them from the monocots, like palms and grasses, which have narrow leaves. That is: broadleaved trees are dicot trees.
But as outlined in Chapter 6, the dicots are no longer perceived as a single, coherent group. They include a mixed bag of primitive types, such as magnolias, peppers and waterlilies, which are presumed to resemble the ancestors of all flowering plants; and they also include a particular, more modern group, a true clade, known as the ‘eudicots’. What I am now calling ‘thoroughly modern broadleaves’ are the eudicot trees.
The eudicots are the most varied plants of all. They range from tiny floating duckweeds, through a host of herbs and scramblers and climbers, to some of the world’s mightiest trees. To look at them, you would see no reason to suppose that they all arose from the same ancestor, and that they indeed form a true clade. But as is so often the case in taxonomy, it’s the small, cryptic features that betray true relationships. All the eudicots have a characteristic kind of pollen which has three slits in it, and is known as ‘tricolpate’. The eudicots have other features in common too, of course; and their DNA confirms their general relationship. But the feature that pins them down, shows them all to be of the same broad lineage, is the tricolpate pollen. Different authorities divide up the angiosperms into different numbers of families but most agree that there are about 450, and that most of these belong among the eudicots. So there are at least several hundred eudicot families which, you may well feel, is too many to keep track of. Fortunately, however, these families are further grouped into orders of which Judd recognizes thirty-one. This, I hope you will agree, is a manageable number.
As you can see from the figure on p. 159, fifteen of the thirty-one eudicot orders form a true clade, known as ‘the Rosids’: not that they are all particularly rose-like, but they do include the order of the roses, the Rosales, and the grouping has to be called something. Another ten form the group known as ‘the Asterids’: this time named after the Asterales, which include the family Asteraceae, which were formerly known as the Compositae, and include the daisies. But six of the thirty-one eudicot orders belong neither to the Rosids nor to the Asterids, and again can reasonably be seen as primitive outliers (‘primitive’ being a relative term: they are not primitive relative to magnolias, but they are primitive relative to daisies). This chapter deals with the six primitive orders of eudicots. The next chapter looks at the rosids, and the one after that is a rapid survey of the asterids.
Of the six outlying orders (neither rosids nor asterids), two contain no significant trees. The Ranunculales is named after the buttercups. It does include some shrubs – for example the berberries – and a few trees among the moonseed family, but nothing that need delay us (though one of the moonseed family provides curare, much favoured for poisoned arrows, and now deployed in medicine as a muscle relaxant). The other order without trees is the Polygonales, which include the families of rhubarb and dock, and of the insectivorous sundews. The four orders of primitive eudicots that do include trees are as follows.
Grevilleas, Macadamias, Planes and Box: ORDER PROTEALES
The Proteales, as now defined by Judd, is highly intriguing. Of course the order includes the Proteaceae family, for which is it named. The root of the name is the same as in ‘protean’; it implies an ability to change shape, and indeed young Proteaceae typically have juvenile leaves that are markedly different in shape than those of the mature plants. The family contains over 1,000 species, in sixty-two genera, spread throughout the southern continents, with occasional encroachments into the north: South America (whence they have spread to Central America); sub-Saharan Africa; eastern India; all of China and South-East Asia; Australia and New Zealand. Many Proteaceae are beautiful, like the bottlebrush trees of Australia that drip with nectar: Banksia, and the pincushion-flowered Hakea. The Protect flowers of South Africa’s upland fynbos, huge and flamboyant and good for drying, alone justify the journey (the beauty of the landscape is a bonus). Quite a few of the Proteaceae, too, are fine trees. Among them are Macadamia integrifolia of Australia, source of the egregiously hard but excellent nuts, which are a staple for many traditional Aborigines and are also the only native Australian food plants of significance to world markets. The Rewarara of New Zealand (Knightia excelsa) which grows up to 40 metres, has juvenile leaves that are long and thin and mature leaves like a chestnut’s, though thicker and glossier. Australia’s Grevillea robusta is
a magnificent timber tree confusingly known as the silk oak and sometimes even as the golden pine (while other trees are also sold as ‘silk oak’). It is also widely grown in India as a shade tree in plantations of tea and coffee, both of which grow best when not too exposed; and its leafy branches when trimmed make fine cattle fodder.
It is a taxonomic novelty to find the plane family, the Platanaceae, in the Proteales order; yet DNA studies show this family to be close to the Proteaceae. There is only one genus, Platanus, with about ten species, but it’s enough to leave fine scope for confusion; for to the British Platanus are the plane trees, while the Americans call them sycamores (though some are also called buttonwoods). To the British, the sycamore is Acer pseudoplatanus – meaning ‘maple false-plane’. (Just to stir the pot a little further, the ‘sycamore’ referred to in the Bible is a species of fig, in the genus Ficus.) In any case planes make fine ornamental trees especially in cities (they shed their bark and the soot with it) and in North America their timber has been used for everything from barrels and butchers’ blocks to fine veneers; while the Native Americans of the east used planes for dug-out canoes, one of which was reputed to be 20 metres long and weighed four tonnes. Planes grow wild throughout the south-eastern United States, and also in the eastern Mediterranean, north India and China. Given that Platanaceae is closely related to Proteaceae, and Proteaceae is obviously Gondwanan, the southern supercontinent), where did the Proteales as a whole originate?