by Colin Tudge
WHO’S WHO AMONG THE CONIFERS
The classification of conifers has wavered a little these past few decades. A common traditional taxonomy recognized eight families: Araucariaceae, Cephalotaxaceae, Cupressaceae, Pinaceae, Podocarpaceae, Sciadopityaceae, Taxaceae, and Taxodiaceae. Most modern taxonomists, however (including Aljos Farjon) merge the Taxodiaceae with the Cupressaceae, reducing the list to seven. But some (including Dr Farjon) divide the Podocarpaceae into two – splitting off the ‘celery pines’ into the Phyllocladaceae. So now we are back to eight.
Note, in the following account, that three of the eight families contain only one genus, and only three families contain more than ten genera: the Cupressaceae with thirty, the Pinaceae with eleven, and the Podocarpaceae with eighteen. In all Dr Farjon now recognizes seventy genera – many with only one or a very few species. This is typical of ancient groups that have found just a few niches in the modern world – ‘few’ being a relative term that in practice means extensive and various.
Of the eight families, the Podocarpaceae live mainly in the southern hemisphere, and the Araucariaceae is exclusively southern. The rest are primarily or exclusively northern (although of course human beings have introduced trees from all families to just about everywhere). In the deep past all the world’s landmasses were grouped in two vast supercontinents, Gondwana to the south and Laurasia to the north. So it is tempting to speculate that the Podocarpaceae and the Araucariaceae originated in Gondwana, and the other families in Laurasia. But their places of origin are far from certain. In the past, as we will see, there were araucarians in the north as well as the south – the south is where they just happen to have survived. The modern cypress family, Cupressaceae, occurs all over the world. I like the idea that the Araucariaceae and Podocarpaceae are Gondwanan, and perhaps the Cupressaceae, and that the rest are Laurasian. But I have sometimes been forced to acknowledge that some of the things I would like to be the case, aren’t.
The relationships between living conifers, and between the living and the extinct, are not easy to pin down. Morphology (structure) is the main guide to relationships, but the various conifers seem to have too few distinctive features, and sometimes the most important structures – like the cones of podocarps – are too reduced to make much sense of. Often it is hard to decide whether any one particular feature is ‘shared derived’, and signifies close relationship, or is merely ‘primitive’, and common to everybody. Molecular studies should help to clarify things, but as yet there seem to be too few. So it is not yet entirely clear whether the various conifer families, as now recognized, all form truly coherent groups (true clades); and it is far from clear how and to what extent the various recognized living families relate to each other. Thus some show the Pinaceae as outliers – the sister group of all the rest. But others group the Pinaceae with the Podocarpaceae and Taxaceae. I have described the families in no special order.
Kauris, the Monkey-puzzle and the Long-lost Wollemia: FAMILY ARAUCARIACEAE
The Araucariaceae were very various in dinosaur times (245 to 65 million years ago), and they lived all over the world. Now there are just forty-one species left, in three genera – Agathis, Araucaria and Wollemia – all in the southern hemisphere. The greatest variety of Araucariaceae is on the magical Pacific island of New Caledonia, perhaps the most pristine remaining fragment of ancient Gondwana.
Among the twenty-one species in the genus Agathis is one of the mightiest trees of all: Agathis australis, the kauri of New Zealand’s North Island. The grandest of the grand is Tane Mahuta: it is 51.5 metres tall, its lowest branches are nearly 18 metres above the ground, and its trunk is 13.77 metres in girth – nearly 4.5 metres in diameter – which means it would touch all four walls if planted in an average suburban living room. I have stood at the huge buttressed feet of Tane Mahuta. It is surrounded by other enormous trees, but it makes them seem ordinary. Its trunk rises out of the gloom like an iceberg in the Southern Ocean. The mass of epiphytes it holds aloft in its great spreading boughs is a fantastical, floating garden. It must have supported entire dynasties of lizards and invertebrates who never went anywhere else and must have thought, if they could think at all, that Tane Mahuta was the whole world.
Tane Mahuta is reckoned to be around 1,500 years old. Yet until 1886, when it was destroyed by fire, there lived another kauri known as Kairaru that was more than 20 metres in girth, and was thought to be at least 4,000 years old. Small wonder that the Maoris revered the kauri tree – ranking it second only to the totara, of which more later. They never felled one without a ceremony in which they asked forgiveness – although, as a Maori lawyer remarked to me somewhat wryly, ‘They must have held an awful lot of ceremonies’, for they used vast quantities of kauri timber for houses, boats and carving, chewed its gum and used it for starting fires: they felled whole forests. Fossil kauri gum is still there to be dug up: a form of amber. The Europeans were even more rapacious and reduced the kauri’s range from around 1.2 million hectares to around 80,000. Now New Zealand is protecting its native trees. To walk through a natural New Zealand forest with its spooky battalions of understorey ferns, and with little fantail birds to lead the way is one of life’s delights – and a very accessible one, since the New Zealanders have built so many easy paths, with wooden bridges to span the protruding roots and raised causeways to avoid crushing the wet places and for the kiwis to pass underneath. (Kiwis, flightless and indeed wingless, prowl by night. They hunt for worms and other invertebrates not by sight, as most birds do, but by scent.)
There are Agathis in Borneo, too, in tropical rainforest; and in New Caledonia there are five species, all endemic. By conifer standards Agathis is a fairly recent genus: the oldest date from about 65 million years ago.
The genus Araucaria, for which the whole family is named, has nineteen species of which no fewer than thirteen are endemic to New Caledonia – meaning they occur nowhere else. New Guinea has several Araucaria, too, and so does Australia. Well known in Europe and America – though not too far north (except as an unusual houseplant) because it’s tender – is the beautiful Norfolk Island ‘pine’, Araucaria heterophylla, that grows straight as a Christmas tree but with branches that curl up at the ends; much favoured in the prestige gardens of embassies and smart hotels in warm countries the world over. But the araucarias best known to northerners are the only two species that are native to South America. The monkey-puzzle tree (aka Chile pine), Araucaria araucana, from Chile and Argentina, was once a favourite in suburban gardens (and is still hanging on there; many only just coming in to their pomp). The leaves of the monkey-puzzle are leathery and spiky, and cling closely to the stems. Perhaps they do give monkeys pause for thought – but monkeys did not appear in South America until about 30 million years ago, and the genus Araucaria, apparently far older than Agathis, was around about 120 million years before America had any monkeys at all. Perhaps the monkey-puzzle had no thought of monkeys but evolved its daunting leaves to deter dinosaurs. (So, at least, some botanists have speculated. Certainly, trees are incomprehensible until and unless we consider their past.)
The monkey-puzzle has poor timber, but the Parana pine (Araucaria angustifolia) is much loved by do-it-yourselfers for its lovely variable colours, from smooth creamy white to chestnut brown and rich streaky red, tough but not too tough to work with tools of ordinary steel. The Parana pine grows mainly in Parana, Brazil, and also in Paraguay and Argentina, as a flat-topped tree up to 40 metres high with a straight clear bole around 1.2 metres in diameter. It is sometimes known as ‘Brazilian pine’, and is Brazil’s chief timber export.
Wollemia, the third remaining genus of this once great family is the archetypal relict – to be ranked with the coelacanth, the ancient lobe-finned fish that was found in the ocean depths near Madagascar in the 1930s. For until 1994 Wollemia was known only from fossils, dating from 120 million years ago. Then a group of thirty or so turned up at the bottom of a canyon in the Blue Mountains of New South Wales, Australia.
They were growing alongside flowering trees by a stream. They don’t seem to be holding their own in the wild and must now be actively conserved. Finding Wollemia was not quite like finding Tyrannosaurus rex, but it is conceptually similar.
Nowdays there are no Araucariaceae in Africa, although the fossils show they were there in the past; or of course in Antarctica, where they once abounded; or in the northern hemisphere as a whole, though they were once widespread there. Truly they are a relict group, and we should be grateful for the survivors.
The Plum Yew and Other East Asians: FAMILY CEPHALOTAXACEAE
Here is another archetypal relict family with only one genus – Cephalotaxus – and just eleven species. It grows as an understorey tree – a shade lover – in temperate forest on mountains, mixed with flowering trees, from the eastern Himalayas through China, Japan, Taiwan, Thailand, Vietnam and Malaysia. Cephalotaxus are vaguely yew-like to look at (and in less sophisticated days were sometimes classed with the yews). They are known to Western gardeners by a variety of names that include ‘cow’s-tail pine’, because everything with dark-green needle leaves tends to be called a ‘pine’ sooner or later; and ‘plum yew’, because the female cones of Cephalotaxus give way to a single, soft-skinned seed that looks roughly like an olive – or an unripe yew ‘berry’.
Cypresses, Junipers, Swamp Cypresses and Redwoods: FAMILY CUPRESSACEAE
The Cupressaceae is the only conifer family that occurs all over the world, in all continents (except Antarctica) and both hemispheres – it is impossible even reasonably to guess whether the family arose in the north (Laurasia) or the south (Gondwana). Cupressaceae also has the most genera of all living families of conifers – thirty – although not the most species (just 133). Yet its relict status shines through, for eighteen of those genera contain only one species. In each of them, the once possibly startling diversity hangs by a thread.
The family Cupressaceae has been extended in recent years. In its earlier form, it included only the cypresses, junipers, the Australian Callitris and the thujas, which look like cypresses. But botanists had suspected for many a decade that there is no clear distinction between the Cupressaceae and the trees that were then placed in the Taxodiaceae – the swamp cypresses and the redwoods. Their cones are similar in significant details (not least in the way they develop), and the bark of a big cypress – thick, soft and stringy – is indistinguishable from that of a redwood.
Now it is clear that the old-style Taxodiaceae is not a coherent grouping. Really it’s just a group of genera that look roughly similar because they share primitive features – not because they have any special, close relationship. In fact the various members of the Taxodiaceae are no more closely related to each other than some of them are to the old-style, narrowly defined Cupressaceae. The newly discovered Metasequoia seems particularly close to the cypresses. Thus the traditional Taxodiaceae family may be compared to reptiles or the bry-ophytes – not a true group (a clade) but a ‘grade’: a collection of creatures with similar general features. So the old-style Taxodiaceae are now combined with the old-style Cupressaceae to form a new, expanded Cupressaceae family. However, you will still find the traditional name ‘Taxodiaceae’ on labels in botanic gardens. These things take time to catch up.
Between them the trees of the newly expanded Cupressaceae family live in an extraordinary variety of places. Some, like Chamaecyparis, Fitzroya, Sequoia and Thuja, prefer very wet and tall forests on coasts. Others (Chamaecyparis, Cupressus cashmeriana, Taiwania) live in monsoon cloud forest high in mountains. Some (Callitris, Juniperus) thrive at the edge of deserts. One – Cupressus dupreziana – survives right in the heart of the Sahara where there is virtually no rainfall, drawing its water from a fossil aquifer far beneath the surface. Some junipers live at the edge of the Greenland ice cap, in permanent snow. The various trees in their various habitats are correspondingly various in form: from the very squat, like Microbiota, which hugs the ground for survival in the Russian Far East; to the giant redwood (Sequoia sempervirens), which basks in the mists of coastal California, and is the tallest tree of all. The Cupressaceae family also includes some of the world’s oldest living organisms – in the genera Fitzroya and Juniperus. Like the pines the species of the cypress-redwood family are generally happy in poor soil – and some grow from crevices in rocks, apparently without soil at all.
The old-style Cupressaceae family included twenty-two genera. Most of them contain only very few species, and some only one. Callitris is one of only three genera in the family that contain more than ten species. In fact it has fifteen, of which thirteen live in Australia (two in Tasmania) and two (inevitably it seems) in New Caledonia. In general Callitris favour upland semi-aridity, and grow alongside eucalyptus as ‘fire climax’ species: the kind that thrive when everything else is burnt out. Callitris preissii (aka C. robusta) finds favour as a garden tree sometimes known as ‘cypress pine’.
The sixteen species of Cupressus are the ‘true cypresses’. Between them they span the northern hemisphere, happy on temperate, moist coasts or in desert or high mountain. In south-west North America one species extends down into Honduras. Cupressus dupreziana, as we have seen, hacks it out in the Sahara. The ‘classic’ cypress of the Mediterranean and the Middle East is Cupressus semper-virens (‘always living’). Some Cupressus are native to the Himalayas and western China. But in the Mediterranean and Asia in particular it is hard to decide which are truly native, because so many have been moved and replanted since Roman times, or perhaps even earlier. Calocedrus decurrens from western North America has the nostalgic niff of school classrooms (at least as they were in my day), for its soft, fine-textured timber furnishes 75 per cent of the world’s pencils.
The genus Cupressus should probably be extended to include the six species of Chamaecyparis; either that, or the two should first be combined and then split up again in new ways. The features that are commonly used to tell the two genera apart – notably the arrangement of the leaves – do not seem to carry enough weight, when taken with other characters. Species of Chamaecyparis grow in North America and eastern Asia as tall trees in temperate mixed or all-coniferous forests, from sea level to the mountains. Best known is the garden favourite Chamaecyparis lawsoniana, Lawson’s cypress (aka ‘Port Orford Cedar’) of south-west Oregon and north-west California. In Britain it is often grown as a hedge. In America (though not in Britain) it is acknowledged as a fine timber tree for furniture, ships, oars, paddles for canoes, and church organs. Leyland cypress or leylandii (x Cupressocyparis leylandii), which grows so fast and casts the shadows that cause so much suburban strife, is a hybrid of Chamaecyparis nootkatensis (aka ‘Alaska cedar’, originally from the coast of north California and Alaska) and Cupressus macrocarpus. Apparently the hybrid first arose in a garden in Montgomeryshire, on the English-Welsh border, at the end of the nineteenth century. The fact that these two hybridized so readily is another reason for thinking that Chamaecy-paris and Cupressus should not be treated as separate genera. But as a further complication, Aljos Farjon and others have proposed that Chamaecyparis nootkatensis, together with a newly discovered conifer from Vietnam, should be placed in a new genus, Xanthocyparis.
Fitzroya now contains only one species – the cypress-like F. cupressoides – but it’s a great one. It is native to the coast and up into the foothills of the Andes of southern Chile and Argentina (a wonderful place to see trees) and given time, it becomes massive. But it needs a great deal of time: the oldest living Fitzroya that can be aged are at least 3,600 years old – but there are hollow ones, too, even bigger and undoubtedly older, although (because they are hollow) their age cannot be directly measured. Sometimes Fitzroya grows with its own kind, in groves, and sometimes intermingled with the southern beech, Nothofagus.
Juniperus is the biggest genus of the Cupressaceae: its fifty-three species account for nearly 40 per cent of the whole family. Apparently (like some groups of pines) the junipers have radiated to form many new species in (geol
ogically) recent times. Some live to several thousand years. Between them they span the northern hemisphere – and J. procera is found south of the equator in east and south tropical Africa. They seem to tolerate almost anything from subarctic tundra to semi-desert, taking all forms from ground-hugging shrubs to tall trees: virtually all are drought-resistant. On mountains, some junipers grow to the topmost limit of the treeline. J. brevifolia is endemic to the Azores – and is the only conifer established on any mid-oceanic volcanic island. Its juicy ‘berries’ must have been taken there by birds. J. communis is the most widespread conifer species of all, and has even put in an appearance as one of Britain’s three (possible) native conifers. Juniperus as defined here includes Sabina, a name that still features in many texts and may turn up on botanic labels but does not seem to be distinct enough to warrant generic status.
The most widespread of all conifers: one of the many junipers
Thuja are long-lived and cypress-like. The grandest of all the five species is Thuja plicata, known confusingly as the western red cedar – the ‘cedar’ of the timber trade: fabulous all-weather wood that makes fine garden furniture and shingle roofs that will last a lifetime without further preservation. For good measure too its timber (as in most species of Thuja) is aromatic, and its leaves when crushed smell of pineapple. In its native Oregon, Washington and British Columbia, western red cedar grows to 60 metres, with great buttressed bases that can be 10 metres across. The native Americans of the north-west coast salvaged its long-dead trunks from the swamps and hollowed them into vast canoes and totem poles; and the Haida Indians of the shores of southern Alaska carved arrows from the stems, fashioned the tough knots into fish-hooks, and wove the fibres from the bark into ropes, baskets, mats, clothes and hats. In more humble guise, western red cedar features in suburban gardens, filling the same kind of role as Lawson’s cypress. But the first Thuja to make it to Europe – to Paris, in the sixteenth century – was America’s other native: the smaller T. occidentalis from the eastern states.