Contents Page 4 Introduction 5-6 Chapter 1; Large common liverworts
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| 10.Ethics
Victorian botanists and plant lovers, especially fern and orchid fanciers, scoured the countryside, aided by the newfangled railways, digging up rare and curious plants to grow in their gardens, or in some cases, to sell. Commercial nurserymen stripped whole areas of rare or desirable species. Populations of some native British plants, it is believed, have never recovered. The interest in mosses also increased greatly in the nineteenth century, and a Moss Exchange club was organised. Members held excursions and collected herbarium specimens, which they sent in annually, for an exchange with other enthusiasts. The custom continued until the late 1960s when, for conservation reasons, it was discontinued. I revived plants in a few such exchange packets, and even now, still have one or two growing. Though a commercial market never developed for mosses, this exchange certainly put temptation in the way of any contributor finding a rare or unusual moss - the temptation to collect as much good material as possible. The rarer the plant, the greater the temptation, and the greater the bargaining power of the specimens. One such moss, Cyclodictyon laetevirens, was deliberately and repeatedly collected from its only known site in Cornwall. When it became extinct, the rarity value of the herbarium packets inevitably increased still further. Similar barbarisms are committed on a far greater scale today, by those who plunder tropical orchids, birds, or even butterflies, serving a market in which endangered species often fetch hugely inflated prices. Cyclodictyon laetevirens is rare or occasional on wet deeply shaded rocks in Western Ireland, and recently found in north Devon. It is related to the larger and commoner Hookeria lucens, but is an attractive plant in its own right. It grew fast and well here until 1996, on wet shaded peat or granite, in high humidity, and fruited in autumn. Yet these exchanges were valuable. In an age with few textbooks, knowledge could best be gained from actual specimens, and contributors could study a greater range of plants than they might ever gather personally. The contributors laid the foundations of our modern knowledge. Even now, when looking at hard-to-name species or unusual material, there is no substitute for a comparison with reliably named herbarium plants. A herbarium packet also expresses one of the most basic principles of science in general, and of botany in particular - that a permanent record should be made of any plant or event of interest. Only a minority of amateur plant growers keep such records, yet cultivated wild plants become scientifically worthless if their habitat details are lost. A collection of mosses and hepatics - almost all of which are likely to have been collected from the wild - will have no scientific value unless a secure record is kept of their origins, backed up, whenever possible, by herbarium specimens. Mosses are almost uniquely convenient plants for making into herbarium packets. They are small and easily preserved in a dry state. A half sheet of plain A4 paper is all that is needed. Such a herbarium packet provides a permanent record. It should usually contain some of the actual plant and (in my opinion, equally informative) a fragment of the soil or substrate on which it was growing. On the top of the packet should be written the name (if known) the location, and a brief description of the habitat, perhaps a map reference, a date and collector's name, and also perhaps, a comment on the distinguishing features of the species, and a note or sample of any associated plants. Details of how the plant is being grown, and of how it responds in culture, can also be conveniently written on later. The slow accumulation of millions of such packets, all over the country, over the decades, can become any museum curator's nightmare. I had about 40 shoeboxes full, many of which I never looked at again. They were given to Reading University botany department when we moved in 2002, and 99% of them will never be of any use to anyone again. The problem is - I have no idea which 99%, It can be sad to look at the faded yellowing specimens gathered by past generations of botanists. Yet hidden in even these ancient packets may be valuable information, undreamed of by those who collected them, or as yet unknown. For instance; most years, one or two species of moss or hepatic are still being added to the British list. Some are plants which have been confused with close relatives, and are only distinguished for the first time by careful comparison of living plants, and by combing through old herbarium collections. Some are genuine new discoveries, and some are recent arrivals, introduced from elsewhere in the world. Their origins, their history and their distribution, can often be traced by looking in those dusty drawers and boxes. On of the greatest problems for botanists in Third World countries is that the herbarium collections made by pioneering botanists are usually in a First World country. Among them are often first gatherings of new species. They may be the type specimens on which the original descriptions were based, and without access to them, many plants (not just mosses) are impossible to name. The loss of millions of specimens in Berlin in 1945 still causes problems for botanists, including bryologists. Some countries are now reluctant to allow herbarium specimens, even of mosses, to be taken away, and many insist - rightly - that duplicates be left in their own land. Apart from their usefulness to bryologists, these packets may contain information of wider interest. Nineteenth century gatherings made from trees in England contain luxuriant material of species now rare or extinct, and provide dramatic evidence of the disastrous effects of air pollution during the Industrial Revolution. Among the greatest dangers to the human race today are the greenhouse effect, the rise in carbon dioxide levels, and the damage to the protective ozone layer in the upper atmosphere. How real are these changes? How have mosses beem responding to them? How will they respond in future? And what about the rest of the planet? Some of the answers may well lurk in those old herbarium packets. Old gatherings of Bryum argenteum from the Antarctic, for instance, provided evidence in the1990s that the ozone layer was being damaged, and ultra-violet light levels increasing there, before direct measurements began. The first moral than, is clear. If you become seriously interested in these plants, you will make many collections of possible scientific value. Label the cultures securely. Keep a record and a herbarium. Keep them methodically, and keep them in a safe place. A tedious topic, and one often neglected, is the labelling of living plants. It is more essential even than labelling a herbarium and keeping a catalogue - if the cultures are to retain any scientific value. Yet it is not easy. There are practical problems. Plant labels - for what they are - are expensive. Chinagraph fades, Indian ink cracks, plastic goes brittle in sunshine. For what it is worth, my own eway of labelling may be of interest. I use floor tiles, the flexible ones, as found in Homebase, etc., but choosing those without an adhesive backing, when I can. They are cut into label-sized pieces with scissors. This is hard work unless the tiles are first softened, by soaking in hot water. Why bother? Because you can then write on both sides with an ordinary sharp lead pencil, and the writing is permanent - at least up to 20 years, perhaps more. The tiles come in several colours, so plants can be colour-coded. I use red labels for tropical plants, yellow for Mediterranean ones, and so on. You can make them any size or shape you want. They can even be cleaned with an abrasive cleaner ("Vim"), and re-used. No commercial labels I know of have all these advantages. Even so, labels get lost, or have accidents. They fall out of pots. They get covered with algae. Passing snails graze on the algae, and their rasping tongues remove the graphite writing - and the information too. Lime deposits may obscure them. Mosses may grow over them (many mosses grow better on the labels than on the substrate provided!), or chemical reactions in wet soil may stain them with a dark deposit. It is a regular chore here, to check for faded or missing labels, and to replace them. Sometimes their information has been lost, and must be recovered from another source. I put most of the information on the herbarium packet onto the label as well. It may be written very small. It may be illegible to everyone in the world except me, but so long as a few words, or the number, or even part of the number, can be deciphered, the rest of the information can be recovered from the catalogue or, less conveniently, from the herbarium packet. Labels with nothing but a name or number on, as seen in many collections, are less informative for a visitor. Also, if labels carry only the minimum of information, it is far harder to replace that information, if any of it be lost. At a more practical level, I always have a good stock of fresh labels and a sharp pencil to hand. Otherwise, human nature being what it is, I would more often succumb to the temptation, when making a transplant or a new culture, to "leave the labelling till later". I have over 600 species of bryophytes still growing, in over 2,000 cultures, and have managed to restore the labels on over 99% of them since my illness. Yet if only 1% of these labels were lost annually, any long-term scientific value these cultures might have would be greatly diminished. There is the legal and ethical position of anyone who picks wild plants to consider. Parts of this book are an incitement to break the law. Technically, it is illegal to uproot any wild plant - even a tuft of moss - without the permission of the landowner. The total enforcement of such a law would make it illegal even to pull up a piece of chickweed. In Germany it is now illegal to collect the commonest species of Sphagnum or Dicranum. This ridiculous law has annoyed many botanists. Yet the responsibility remains, not to gather mosses without conserving such information as they might provide. Even the most experienced bryologist often cannot name some difficult species at sight, but needs to check them microscopically. A beginner can spend frustrating hours trying to name even common ones. Yet the time spent naming them, and the time which may be saved by keeping the specimen for comparison another time, gives even packets of the commonest species some value. They should usually be kept. A bryologist who behaves responsibly is unlikely to endanger any rarities by collecting them, except in a few places which a beginner is unlikely to discover unaided. A Victorian gardener stealing wild ferns or orchids had to take a complete plant. A Victorian moss-hunter would take the best material to fill his herbarium packets, but when collecting from a restricted habitat like a single tree or a small rock outcrop, it is easy to remove most of the population of any species. Nowadays, there is rarely any excuse for gathering more than a few shoots, even if it is obviously abundant. This is even truer for someone who intends to grow the moss. I have, on occasions, grown cultures from a single shoot. It can be done. It is also worth remembering that many habitats are more likely to be damaged by heavy boots than by acquisitive fingers. Sphagnum bogs are especially vulnerable to trampling. Fortunately, the average walker avoids squelching into them. Victorian fern collectors, even if they often collected wild plants in a way we now think unacceptable, did at least develop the skills of keeping them alive, and propagating them. Some of their cultivars still survive. For some reason, there never grew up a similar tradition among members of the Moss Exchange Club, of growing mosses and hepatics. Perhaps there were just too many species, and too few enthusiasts. Members' efforts were concentrated almost entirely on finding, naming and describing them. Indeed, the idea took hold that mosses and hepatics were far too specialised to be kept alive, let alone grown well. When a new or rare species was found, a herbarium packet at lest guaranteed the survival of the scientific evidence. It is still expected, when a species new to the country, or to a county, is found, to make a herbarium specimen (however small) which must be checked by a referee, and deposited as a voucher specimen. I have had several extremely rare British mosses growing here, some of them known only fromone site, or from one small area. They do not seem different from their commoner associates of similar habitats, or more "difficult". Embarrassingly, several were given or collected in 1995, shortly before my illness, though these too have survived. Yet because even the commonest mosses are so rarely grown, there is virtually nobody who would feel confident about keeping and propagating such rarities. Anyone who has worked through the suggestions in the earlier chapters of this book, and successfully kept most of the commoner species they mention, would bein a far better position to do this. Growing rare or endangered flowering plants, at least, has become a more acceptable idea in recent years. However, if the hope is to contribute to their conservation, it can only be a short-term measure. A private collection cannot last longer than one human lifetime, and even the most prestigious botanic gardens may lose plants over the years, through neglect, misfortune, or changes of personnel. Yet private collections are a huge resource, and a reservoir of horticultural skills which could be used far more, to conserve and propagate plants - even mosses - diverting some energy perhaps, from the keeping of millions of boringly similar garden and greenhouse plants. There exist organisations which link private collectors together, in which plants are freely exchanged and given away, and whose members accept, in return, certain responsibilities. Their object is to create and maintain a permanent network of collections in which endangered garden varieties and cultivars, and sometimes also wild plants, are systematically exchanged and propagated, and their future assured. There are a few very rare or endangered British mosses and hepatics which have legal protection. To collect them without a licence is now a criminal offence. In some cases, their long-term management plan includes setting up a reserve population in culture. But who is going to do that? Who has the necessary experience, even with commoner ones? Most specialist plant societies have informal plant exchanges, and are served by dedicated commercial growers who rarely make much money, but who have, and provide, a lot of enjoyment, by propagating promoting and selling the newest, the rarest and the most fashionable plants they can. Nothing remotely like this has ever happened among bryologists. Perhaps - some day - it will. Even so, more than once, I have persuaded someone else to grow a moss, lost it myself, and then scrounged a piece back again. The truth of one old gardeners' proverb is self-evident. The best way to keep a plant is to give it away. Anyone who becomes seriously interested in mosses and liverworts will certainly wish to join the British Bryological Society. Details are in the Appendix. Another conservation possibility is to re-introduce extinct or threatened plants to suitable habitats. This is an unusual and often controversial thing to do. Certainly, sites of outstanding scientific interest - which may be the only suitable places for such plants - should never be tampered with in this way, except after consultation with the Nature Conservancy Council, and with those who manage the site. However I can see no objection to introducing endangered plants to to less elite habitats, even perhaps to a garden. It would be quite irresponsible to collect wild material of any except the commonest species for such transplant experiments, without a considerable knowledge of the plant and of the habitat concerned, and of how to grow mosses generally. I mentioned a few introductions to my garden in Reading. All these survived until 1996, without attention for five years. A well-judged introduction, unlike a greenhouse culture, may persist for decades without any maintenance. However there is generally little scope for introducing mosses to a garden, other than those which might occur anyway, unless an appropriate habitat can be created for them. Otherwise, it would be out of the question to gather wild material of any except the commonest wild plant for this purpose. However, as chapter 6 suggested, there is no reason why one should not create a habitat, say a backyard Sphagnum bog, or a mud-capped wall. A retired Oxford botanist, for instance, maintained a "traditional" Oxfordshire stone wall in his garden, by putting an annual dose of lime-rich soil on top. On this, a few characteristic mosses, such as Encalypta vulgaris persisted, though they were dying out elsewhere in the county, as people stopped maintaining such walls. I had about thirty kinds of mosses in my Reading garden. Less than half were introduced, and most introductions died out. Yet, despite the dry polluted climate, there were some surprising successes. For instance, spare bits from greenhouse cultures were put on low brickwork at the edges of garden beds. Pleurocarps of warmer and drier climates, and of lime-rich rocks and soil grew best, notably Eurhynchium meridionale, a Mediterranean species, very rare in Britain. It could be said that introducing mosses in this way is upsetting the local flora. The reply must be that every gardener who digs up ground elder and plants rose bushes is doing just that, anyway. And of course, garden plants may escape and upset wild habitats. Himalayan Balsam is spectacular along the Thames in summer, and Buddleia has done more to beautify our towns and waste ground than all the municipal park-keepers in the country. Our worst foreign invader has probably been Rhododendron ponticum, which looks good in flower, but swamps everything else, and has become a major problem in many National Parks. Other countries have suffered far worse invasions, such as the Opuntia plague in Australia, and have responded with severe restrictions on the importing or growing of many plants, especially cacti. It is hard to imagine any introduced moss menacing the British landscape or economy in this way. The most aggressive moss introduction so far has been Campylopus introflexus, from the Southern hemisphere. It may have displaced native Campylopus species in some places, but is a striking addition to our flora, and has hardly become a nuisance. I once inquired at a local Customs office in Reading, about getting an import licence for live mosses, as one can do for flowering plants, Someone made a remark (I think facetiously) about checking the regulations for fungi, but otherwise my enquiry aroused no interest. My parcels of mosses have passed unhindered to and fro between several countries, labelled; "Bryophytes; Botanical specimens. No commercial value." However, there is a real danger, not form the plants, but from associated small animals. The voracious flatworms from New Zealand which have colonised parts of the British Isles, notably the Orkney Islands, have devoured and, in some places, almost exterminated earthworms. They are the kind of unpleasant and damaging creature that could inadvertently be introduced in moss tufts and soil. I suggest that anyone growing mosses from other countries should abide by the regulations for growing imported plants - so far as possible. It is impracticable to separate many mosses from the soil in which they are growing. Yet the regulations for flowering plants may require that the plants be treated with an insecticide (I use Derris dust) and be kept under cover, at least for a few months. These are sensible precautions, and anyone introducing foreign wild plants, including mosses, should abide by them. There is one last suggestion about introduced mosses, not only from abroad, but also from other parts of Britain. There are not many people who can identify the more "difficult" species, and there is still a great deal of taxonomic work to be done, even perhaps on the commonest species, and even in the most populated parts of Britain. Therefore, no introduction should be made which might confuse future bryologists, without making a permanent record of it. Striking and easily recognised exotics are no problem, but material of common, "difficult" or variable species like Bryum capillare and Brachythecium rutabulum should not be willfully introduced from distant parts. In countries where the moss flora is less well known, or even in less well-studied parts of the British Isles, it would be unhelpful to introduce any mosses or hepatics at all, unless it were quite certain that nothing like them grew nearby. Similar concerns have been raised about the practice of planting wildflowers along motorway verges - using commercial seed derived from foreign strains of British wildflowers. Finally; anyone who becomes knowledgeable about any aspect of natural history will soon see one of the greatest ethical issues of our time - the conservation of our planet's wildlife heritage, not just in distant rainforests, but also in that patch across the road. The first step in conserving and safeguarding anything is to find it and identify it. To make a full and reliable list of the plants on any site is a valuable skill. For mosses, it is a very rare skill indeed, and one which may take many years hard work to acquire. Even today, in Britain, the most intensively studied country on Earth; good habitats are being destroyed because nobody knows what is in them, or because too few people care. It is the duty of every good citizen to try to stop habitat destruction, even for obscure mosses or unpopular insects, no less than for pretty flowers or cuddly mammals.
In most large English cities, tree trunks used to be a lifeless black or grey, or stained with vivid green algae (Pleurococcus), or perhaps with the khaki-green crust of the lichen Lecanora conizaeoides. Mosses were absent, and on most city trees, they still are. A rewarding moment for anyone from London or the polluted Midlands, is a first look at a roadside trees in Ireland, in west Scotland, or in western Wales, where the air is clean. Here mosses, hepatics, and large conspicuous lichens grow not only on the bases of trees, but high up the trunks and branches, even on the twigs. Ten or more species of moss can often be found on a single tree, some of them rare or absent from polluted parts of Britain. At least three quarters of British people live in places where the epiphytic flora has been largely destroyed by air pollution. Many people found it hard to believe, at first, that these apparently sensitive plants could be kept alive in the centre of Reading. The main pollutant is sulphur dioxide from burning coal and oil. Only unusually high levels of sulphur dioxide damage mosses directly, by bleaching them. It is the habitat which is wrecked. Reacting with rainwater to form sulphuric acid, the gas makes the bark of trees and the surface of rocks too acid to support them. It is very noticeable that acid rocks - slate and sandstone - and acid tree bark - oak, alder and conifers - are most affected, and have the poorest growth of mosses in polluted areas Alkaline rocks such as limestone, and alkaline tree bark, especially elder, sycamore and, where it still exists, elm, are more likely to support mosses and lichens, since they are better buffered against the acid. Even in the dirtiest towns, where tree trunks are devoid of life, mosses may be found on cement, limestone, and asbestos. However, the effects of pollution can be more complicated. An early discovery, from reading literature on air pollution, was that sulphur dioxide is an unstable gas. Inside a house, it is soon absorbed onto surfaces. That is why bronchitis sufferers were safer indoors during the killer smogs of the past. In an enclosed greenhouse or frame, it is unlikely to damage sensitive mosses. Even outdoors, polluted air moving through a screen of trees has much of the sulphur dioxide filtered out. Sometimes sensitive epiphytes persist in sheltered valleys and woods, while becoming extinct all around. Also, average sulphur dioxide levels have fallen in most towns in the past fifty years, and the very high peak levels of the past no longer occur. As a result, the epiphytc flora of the more densely populated parts of Britian has improved, and some sensitive species have been refound, even near London, in recent years. Lead pollution, hydrocarbon haze, and ozone from traffic fumes, whatever their effects on people, are not having the same disastrous effect on epiphytic mosses. In practice, then, air pollution is unlikely to be a problen for most people trying to keep epiphytes in a greenhouse. Yet they are among the most difficult mosses to keep anyway. They are very different in their cultural needs from most flowering plants and terrestrial mosses. Few can be grown on soil. Pleurocarps are the most conspicuous. Hypnum cupressiforme grows almost everywhere. Even the small form with almost straight leaves (now known as H. filiforme), which is common on trees in the West, can be kept on peat, in a clay pot. So can Isothecium myosuroides, which is abundant on tree bases and trunks in woods. In damp sheltered places, many terrestrial mosses can be found on trees, as well as on the ground. They may include Amblystegium serpens, Brachythecium rutabulum, and B. velutinum. On basic bark, Homalothecium sericeum, and more rarely, Neckera crispa, N. complanata and Homalia trichomanoides may be found. The last two both resemble Neckera crispa, but are smaller. In Neckera the leaves are nerveless, and the shoots curled down, Homalia has a faint nerve, and the shoots usually curl up. All can be found also on strongly drained chalk soil, or limestone rocks or old sheltered limestone walls. They can be grown accordingly. They are not as highly specialised as some epiphytes, and do not normally grow on the higher and more exposed trunks and branches. Even so, they grow equally well on neutral or lime-rich mounted cultures of tree bark, given sufficiently high humidity when actually growing. There is a big difference between the acid bark of pine, oak, and alder, and the more alkaline and nutrient-rich bark of sycamore, ash, elder, and elm. In moderately polluted areas, only trees with alkaline bark support epiphytes. I have made many mounted cultures using grated elm or sycamore bark, but it may be as effective and convenient to make mounted peat cultures, and to sprinkle a pinch or two of powdered limestone or finely grated alkaline bark on them, when needed. Epiphytes can of course be kept on pieces of their original tree bark. However, that offers no guarantee of success. Most are drought-resistant, and will survive, even for a year or two, in quite dry conditions. The more specialised ones will soon die if they are kept too moist or shaded, and even more, if the substrate gets soggy. I have kept almost all my epiphytes on grated tree bark or peat, mounted on polystyrene, as described in chapter 7. These little mounted cultures may seem quite fiddly to make at first, but become easy with practice. The substrate should be grated, crushed, or otherwise prepared in a loose dry powdered form. Bark can be grated with a small hand plane or grater, peat sieved to a fine powder, rock crushed with a hammer. To get an even layer of glue, take two pieces of polystyrene, ready cut to size with a razor blade, so they will fit in the flower pot, put some glue on one (I use uhu), and rub the two together, to spread the glue evenly. Press each piece into the powdered substrate, then sprinkle more substrate on top, and press it down with a finger. The object is to get a fairly continuous layer which will not wash off when watered. The mount can stand in a plastic pot, either more or less horizontally or, better for many epiphytes, at a steeper angle, or even vertically, to ensure that water never collects on the surface. It is worth sitting down to use a whole tile, making 30-40. even 50 mounts at a time, and keeping them ready for use When it is used like this, only a small amount of substrate is used, and the nutrients may be washed away by watering within a few years. If so, the moss, now stranded on bare polystyrene, will appreciate replanting, or a little fresh substrate sprinkled over it. Planting the moss is now very easy. The tiniest shoot or fragment can be pressed into the polystyrene with a pencil point, or the tip of a label, or tufts or mats of moss stuck on with a trace of glue. Pleurocarps may be held in place by surface tension, or speared by a Berberis spine, and new shoots soon attach themselves, needing no glue at all. Epiphytes can be very patchy in their distribution. There may be only one or two “good’ trees in a wood, perhaps the oldest or most sheltered ones. The mosses on them should then be collected only very sparingly. It is not necessary to match the bark exactly. Bark from a different kind of tree, or fine peat, will usually do for the planting, but the distinction between acid and alkaline bark should be observed and followed, as noted above. Another useful indicator can be to look at the lichens o a tree. If there are orange lichens present (Xanthoria) , the tree is likely to have alkaline bark, and sometimes, as near a busy road or a dusty lime quarry, even oak or pine can support lime-loving plants. Mosses from alkaline trees should of course be on alkaline bark. They might include the ubiquitous Bryum capillare, or the very similar B.subelegans. A Syntrichia is characteristic of alkaline trees. It is Syntrichia laevipila, resembling Tortula muralis, but with a more solid-looking leaf, and a shorter hairpoint. On older shaded trees, or on elder bushes, species of Zygodon grow, their triangular bright yellow leaves looking like those of a Barbula. With them, or further up the tree in drier positions, may be found Orthotrichum species. Orthotrichum diaphanum is the commonest, and was mentioned as a moss of walls, even in towns. It is the only Orthotrichum with a hairpoint. There are many other species. Other common ones on trees are larger. O. affine often has capsules tucked among the leaves. O. lyellii very rarely fruits, but may have gemmae on the leaf tips, as mentioned in chapter 9. There are several other species, mostly impossible to name without capsules. Growing among them, or on more acid tree bark, except in the dirtier parts of the country, will be Ulotas. Those which grow on trees have leaves which are strongly crisped when dry, and hairy capsules. Ulota bruchii and U. crispa are commonest, and can be hard to tell apart. Capsules are often present. U. bruchii is usually larger. Near western coasts, Ulota phyllantha is sometimes abundant. It does not fruit, but its gemmae are usually conspicuous, and form fuzzy brown tufts on the leaftips, rather than being spread over the leaf, as in Orthotrichum lyellii. It is rare and stunted inland, but may be recolonising places where it was once eliminated by air pollution. It has even been refound recently on Hampstead Heath, in north London. Ulotas and Othotrichums are the most specialised epiphytes, found even on exposed twigs - where the air is clean enough, as in parts of Wales. None has ever succeeded here on soil in flower pots, nor even on pieces of original bark. All are now on mounted cultures. Being plants of exposed habitats, it is not sensible to keep them shaded or constantly moist, yet they dry out within minutes under normal greenhouse conditions. While they can withstand this, and will tolerate frequent drying and wetting better than almost any other moss, they need very high humidity for a easonable length of time, if they are to make worthwhile growth. Indeed, if the air around them is saturated, they can absorb water from the air and start growing without being watered at all. They also seem less tolerant of shade than many mosses. They grew better in Reading after the removal of the two lime trees. They were on a top shelf, with almost full north light, covered with polythene, almost continuously moist from October to March, and only intermittently watered in spring and autumn. In warmer summer weather, the polythene was removed, and they were left quite dry, even exposed to some sunshine. Even under ideal conditions, they are slow-growing plants, hardly spreading by protonema. It takes at least a couple of years for one shoot to make a small tuft. As might be expected, many mosses of bare rocks grow in similar conditions, on similar mounted rock cultures. Pleurocarps which grow on alkaline tree bark are more likely to be found also on rocks, or even on the ground. Some have been mentioned. However there are several rarer and more specialised epiphytes. The least uncommon include; Leucodon sciuroides, on old, sometimes sunny tree trunks. It has narrow creased (plicate), glossy leaves. Near the south coast, Leptodon smithii is locally frequent. Its small pinnately branched stems curl up when dry. Cryphaea heteromalla is more widespread, and of medium size. It has creeping stolons and erect branches, often with fruits sticking out of the side on a very short seta. It needs strongly alkaline conditions, and is often found on elder. Leskea polycarpa grows on muddy roots, tree trunks and stones, by lowland rivers. It is small, a little larger than Amblystegium serpens, but of a pale colour, unlike any other pleurocarp mentioned in this book. It is frequent by the Thames at Reading, fruits freely, and has even turned up, though rarely, on walls and kerbs in the suburbs of the town. These, and other similar rarer species, can be grown on mounted alkaline bark, or on well-drained rock or soil in clay pots, and in rather dry well-lit conditions. They are less critical in cultivation than Orthotrichum. Many lowland rivers provide a rather special habitat, where tree roots or trunks are covered at times with silt, by high or flood water. Though they may look mucky and dirty, such muddy trees and roots often have a very distinctive moss flora. If they are dry, splash a little water on them and any mosses which are present will spring into life. Syntrichia latifolia is likely to be one. The unusual shape of the leaf makes the reason for its name obvious. Like Leskea, it is common by the Thames, and sometimes turns up on sheltered muddy tarmac, and even on pavements.
Lower down a tree root or a river bank may be some other very obvious large mosses. Since they spend most of their lives underwater, they hardly qualify as epiphytes, yet, strangely, some can occur on intermittently flooded trees by rivers, well above the waterline. Cinclidotus fontinaloides has large blunt laves with thick margins, and straggling stems, several inches long. Fontinalis antipyretica looks very different. Its trailing underwater stems, a foot long or more, make it one of the largest British mosses. The leaves are keeled, giving the stems a triangular cross-section. It is a popular aquarium plant. It persists here if treated like an epiphyte. Though it will stand gentle drying in summer, it needs very high humidity, as under a sheet of polythene, to grow at all well. In fishtanks, it makes thin straggly growth underwater. Attached to stones in cold mountain streams may be found the darker more slender F. squamosa, which may be grown likewise, but in neutral water, with no chalk or limestone. Acid trees, notably oak, have a less varied moss flora, except in the remote and unpolluted parts of the country, and in a few ancient forests where beginners should not collect. Yet some of our commonest epiphytes are tolerant of acid conditions. They even became commoner, and perhaps replaced less tolerant species, as tree bark became more acid a result of air pollution. In the South-east, the most widespread epiphyte of all is probably Dicranoweisia cirrata. It is often found on wooden fence posts, and on the bases of suburban trees, making green cushions with twisted leaves. The tufts are darker green, and more compact than those of Ulota, the leaves and stems shorter. The small fruit is usually present, quite hairless, and raised well clear of the leaves. Two small Dicranums, D. tauricum and D. montanum, are less common, but have increased in recent years, on similar acid trees. D. tauricum forms dark green patches on the boles or branches. The leaves, finer than the finest needle, are rigid and brittle. If you lick a finger and press it against this moss, dozens of tiny leaf tips will break off and stick to it, visible through a lens. Dicranum montanum has leaves twisted, and not brittle. It may be confused with the much commoner Dicranoweisia cirrata, but has far narrower and finer leaves. These are small, slow-growing plants, and should be on firmly compressed peat in a clay pot, or better, mounted on acid bark, and rather dry. Except in the most humid ravines in the far West, few hepatics grow on trees. Few are common enough to mention here. Frullania dilatata is the most widespread, in Britain at least, of this large worldwide genus. The dark stems creep flat against the bark. Only through a microscope can its fascinating structure be appreciated. The main leaves are in two flattened rows, one on each side, and each leaf has a little pouch at the base (the “postical lobe”) On the underside of the stem is a third row of smaller leaves, of a quite different shape (the underleaves). Literature about hepatics is full of technical terms, which describe the strange structures and complex, leaf arrangements which these plants have evolved. In western Britain, Frullania tamarisci is even more common, sometimes on every rock and tree. It is rare in the East. It has main leaves less rounded, perhaps slightly pointed, and is often of a brown or purple colour. The easiest rough distinction is that it is very rarely fertile, whereas F. dilatata usually has the distinctive perianth (the sac which surrounds the young fruit), on the ends of some of its branches. Another distinction is that through a strong (x 20) lens, F. tamarisci can be seen to have patches, or a line along the middle of the main leaf, of larger translucent cells, giving the impression of a pale nerve. Radula complanata is distantly related to Frullania, and has a similar leaf structure, but looks quite different. Its pale green stems with rounded leaves are pressed very flat against the bark. In the East, it grows only in damp sheltered woods. Metzgeria furcata is an oddity, a tiny thalloid (leafless) liverwort that grows in quite dry places, even in eastern England. It is quite frequent on the shaded trunks of large trees, especially where water runs down in wet weather. Further west, where the climate is wetter, and the air cleaner, other Metzgerias are sometimes common. They may grow on the smaller branches and twigs of trees, as well as on the trunks, especially in damp valleys and near streams. Both produce abundant small gemmae, by which they spread. Those of Metzgeria temperata are clustered at the ends of the branches, those of M. fruticulosa scattered along the sides. Both need high humidity, as in an enclosed frame, to grow well in cultivation, and are best grown on mounted bark. Yet they also need strong drainage, and tolerate neither deep shade nor sunshine, making them quite tricky to keep. Another genus of hepatics is Lejeunea, part of a huge worldwide tribe of many hundreds of related and often very similar species. In this and related genera alone, there are about 15 kinds in Britain. All are tiny, most are rare, and only L ulicina is likely to be found by a beginner, except in the extreme West. Though hardly larger than a Cephaloziella, it has a complex leaf structure, with tiny pouches, a few cells across, at the base of each leaf. Through a microscope it is a beautiful sight, but in the field can be seen only a pale green stain in the crevices of a tree, perhaps in a sheltered wood. A good lens is needed even to see it, and a knife, to gather a little of the bark on which it is growing. Planting these tiny hepatics on mounted bark is the only way to keep them, but is not difficult. All can withstand gentle desiccation for long periods, if kept humid and shaded. Waterlogging will quickly and completely kill them, as will any exposure to warm sunshine. The mounted substrate should be sloping or vertical, or in a clay pot, to absorb surplus moisture. On the other hand, like all mosses, epiphytes can only grow when they are moist. They need to be sprayed with clean lime-free water, but are so small that, except in moist weather in midwinter, they can dry out again within minutes, even in a quite damp greenhouse, and therefore have little chance to make any growth. Nor do most epiphytes grow well in warm summer weather. When temperatures go above about 30C, as is probable at times in any greenhouse, they are only likely to be weakened, or to go mouldy if kept wet. It is best to keep them always well-shaded and humid, covered in polythene perhaps, but not wet when high temperatures are likely, and slightly moist for the rest of the year, letting them dry out gently at times. Lejeuneas tolerate a combination of shade and warmth quite well. They will grow in an enclosed frame or glass tank, or even in a test tube, in a cool greenhouse, or in a dim light indoors, as described later. Epiphytes are one of several groups of mosses and liverworts which have hardly ever been kept alive before. There is a great range of preferences between them. Leptodon smithii, a southern and Mediterranean species, will curl up and endure fierce and prolonged summer sunshine undamaged, even in a greenhouse. At the other extreme, some hepatics, such as Lejeuneas and Radulas, which are confined to deeply shaded woods, or to the most humid places in the far West, will tolerate virtually no direct sunlight, even in winter.
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