Contents Page 4 Introduction 5-6 Chapter 1; Large common liverworts
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| 8. Chalk and Limestone mosses
Much of southeast England is a chalk landscape, in which acid-loving plants will not normally be found. The chalk turf, close-cropped by sheep, which once covered large areas of our downs, was studded with wildflowers, especially orchids, making it one of Britain’s most attractive wild flower habitats. Now there are often only remnants, many of them protected in nature reserves. The most characteristic mosses of sunny chalk turf are uncommon or small. It may be hard to find any at all in dry weather. The most obvious are Barbulas, Bryums. and common pleuropcarps. They include several garden species, and also the large inflated shoots of Scleropodium purum. In vintage chalk turf, often associated with interesting flowering plants such as orchids and rockrose, more specialised mosses are likely to be found. Most of these are small acrocarps, yellowish-green, and hard to identify. Weissia crispa is one. It is a small plant, the leaves of a bright yellow-green, rather solid, but twisted, and narrower than those of any Barbula. Some pleurocarps are characteristic of chalk. Homalothecium lutescens is one. It has narrow silky yellowish leaves, creased along their length (plicate). Plicate leaves are also a feature of several less common species of Brachythecium, sometimes also found on chalk. Entodon concinnus is very local, but sometimes abundant on warm sunny south slopes, and on sand dune turf. It looks like a miniature Scleropodium. These last two be grown on chalk soil, strongly drained (i.e. in clay pots), and can tolerate long drought and some sunshine, even in a greenhouse. They need reasonable light, and should be kept moist and well sprayed when growing, in at least the cooler months of the year. Shaded chalk turf in thickets and by wood margins may be a more attractive hunting ground. The large and striking Rhytidiadelphus triquetrus is common. With it is often Thuidium tamariscinum, a very common and widespread plant whose large frond like stems make it one of the most attractive and obvious of British mosses. Neither is easy to grow well at first. Both need some shade and strong drainage (use clay pots). In the past I found Thuidium to be very vulnerable to lime accumulation, damaging the shoot tips. It can grow very vigorously on mounted chalk cultures, covered in polythene to give high humidity for at least part of the year. A third striking moss is Thamnobryum alopecurum, which sometimes covers damp glades in chalk woods with a thick springy carpet. It is the largest common dendroid (treelike) moss, with creeping stolons and stiff black erect stems at least an inch tall, sometimes reaching four inches. It is also common on shaded limestone rocks and walls, and on wet rocks by streams in the West. It is hardy and persistent in culture. Under trees, especially beech trees, conditions are very different. Many mosses here are on banks or tree roots, where they are not smothered by dead leaves in autumn. Some of the species may also be found in gardens, and others may be troublesome for a beginner to name. Eurhynchium crassinervum is like Brachythecium rutabulum, but smaller, neater, and usually yellowier, with a more concave leaf. Also worth looking out for is the large leafy liverwort Porella platyphylla, which can form big drooping tufts of a dark dull green on tree roots. It is unusual among liverworts in tolerating dry exposed habitats, even in the Southeast, though it is certainly best kept shaded in culture. It also grows on rocks and walls, especially in limestone areas. The acrocarp Encalypta streptocarpa has blunt dull yellow-green leaves. Though larger than those of any Barbula, they curl up when dry, making the plant hard to see. This too can be kept like the pleurocarps above, dry in summer, on well-drained chalk soil. Quarries may have chalk cliffs, apparently devoid of plant life. However damp chalk faces may have a growth of green algae, making a dark stain which may contain mosses too. A tiny moss in such a place, with narrow leaves, hardly visible without a lens, is probably Seligeria calcarea or the similar S. calycina. In this genus are several British species. They are not very common, and are hard to find, let alone to identify, without fruit, for they are among the smallest of British mosses. These two Seligerias are often found on damp chalk stones or bits of loose chalk in woods, on limestone rock faces, and rarely, even on the damp sides of limestone walls in towns (as in Reading, and in the Winter Gardens in Bath) One cannot grow these tiny Seligerias like normal plants. Take a fragment of the rock on which they are growing, and inoculate small pieces of similar rock by scraping off a few shoots and smearing or squashing them against it. Then wrap it in cling film and keep it moist for a few months. If they take hold, new shoots will appear on the new stone, springing from rhizoids which have penetrated into the porous surface. It can be an uncertain process. I have also grown them on mounted limestone in high humidity, at least in winter. Damp ground on a chalk quarry floor, or damp hollows in shady chalk turf, may support two hepatics. One is a small leafy plant, Leiocolea turbinata. .It needs to be constantly moist, not waterlogged, nor ever dry, and tolerates deep shade. I once kept some on a piece of chalk in a plastic sandwich box for about ten years, with no attention at all, so it should do well on lumps of chalk in a closed jam jar. There are several other species of Leiocolea with a more northern or alpine distribution, which have similar cultural needs. The other hepatic is a leafless liverwort, Riccardia pinguis, with rather shapeless greasy-looking dark green thalli, like those of a small sickly Pellea epiphylla. It may be grown like Pellia, but does not like deep shade, and needs alkaline, not acid conditions. Chalk or limestone country in the West or North, or near the sea, has some conspicuous mosses which are rare or absent in southeast England. Trichostomum flavovirens has a slightly “hooded” leaf, and T. brachydontium a broad solid one, like that of Barbula unguculata, but with a plane margin, not rolled inwards. More widespread on rocks and walls in the West or North, wherever there is a trace of lime, is Tortella tortuosa, with very twisted narrow leaves of a bright pale yellow-green. These, and other British species of these genera, may be grown in strongly drained chalk or limestone in clay pots, in a dry sunny position, and sprayed frequently and kept moist in winter, if not in summer. They also grow well on mounted chalk or limestone cultures. In western and northern Britain, most rocks are acid. Limestone is relatively rare, as are some of the plants which grow on it. Where it does occur, the wetter and cooler climate allows many other lime-loving mosses and hepatics to grow. The largest areas of sub alpine limestone are in the Pennines in Derbyshire, and further north, in the Yorkshire Dales. Their rich and distinctive flora of ferns, mosses and flowering plants make them among the most interesting parts of Britain for botanists. Most of their mosses can be grown by anyone who has successfully kept the commoner southern species. Especially striking is Neckera crispa. The flattened frond like stems with crinkled leaves can be up to two or three inches long, making patches a yard across, or more. They rise up from firmly attached creeping stolons. Though drought resistant, and occasionally found on shaded southern chalk, it is fond of sheltered vertical limestone cliffs, and is best grown in shade and high humidity, in a mounted lime-rich culture. There are also many hepatics of sheltered limestone rock which are rare or absent from the drier South, including species of Scapania, and of the tiny creeping Lejeuneas and their relatives. These must be grown on limestone, strongly drained, in clay pots, or mounted. While they hate waterlogging, and tolerate gentle desiccation, they need shade, shelter, and constant high humidity when actually growing. They should only be collected sparingly, and can be difficult to bring home in good condition. One general point is the importance of good drainage for these plants. Few plants which grow on limestone are likely to thrive in non-porous plastic pots, except Leiocolea and Riccardia. That is to be expected, for limestone and chalk are porous, and usually form well-drained habitats. Yet there are other exceptions. On wet limestone rocks, and in seepages on old walls may be found mosses which revel in wet alkaline conditions, and which, even in habitat, are often encrusted with calcareous matter. One is Didymodon tophaceus, a rather undistinguished moss which can form dull-coloured tufts and mounds where water seeps out of limestone or calcareous clay. It fruits freely in spring. If its habitat were not so different, it could be mistaken for Ceratodon purpureus. It can be kept waterlogged, in strong light like Sphagnum, but on chalk or calcareous soil, it is unusual in growing best in conditions where it becomes encrusted with lime, forming large persistent tufts with a lifespan of 2-3 years. Other smaller and less abundant mosses of similar habitats prefer more shade, and a harder rock, or a mounted substrate. Another general point about soil is worth making here. For these plants, chalk or limestone is essential, but only in small amounts. A pinch of limestone fragments on top of a pot of peat is enough. A lump of limestone from the countryside, or from an old wall, or waste ground, can be kept handy, and broken into fragments with a hammer as needed. Acid soil can easily be made alkaline in this way. However it is no good adding peat to an alkaline soil. The mixture remains alkaline. That, surely, echoes the experience of many gardeners. To grow lime-loving cabbages on acid soil, simply add lime. To grow lime-hating rhododendrons on chalk soil - that is far more difficult. I have found that lime-loving mosses have been slightly more successful and persistent here, statistically speaking, than lime-haters, mosses of peat or acid soil, which have been slightly more likely to have been lost. The slow accumulation of lime from water (even from rainwater contaminated by windblown dust), and from traces of soil splashed around when watering, can slowly raise the pH. of a culture. Hence the importance of using rainwater for watering almost all these plants. Even for the limestone plants mentioned in this chapter, rainwater is usually preferable. 9. Definitions and Descriptions. Some people have difficulty understanding the definitions of cacti and succulents. They will have trouble with these definitions as well. However, one thing is plain. A moss is a moss. There are about 600 kinds in the British Isles, and probably over 12,000 worldwide. Clubmosses are related to ferns, not to mosses. Reindeer moss is a lichen. Neither are mosses. Then things start getting tricky. A liverwort is a hepatic. To be more precise, the plants commonly called liverworts, the large Marchantias and suchlike, as described in chapter one, are large leafless hepatics. Most hepatics are small, and have leaves. There are about 300 kinds of hepatic in the British Isles, mostly with leaves. Many are very rare, or confined to extreme western or alpine habitats. Some are so minute, they are unlikely ever to be noticed except by an expert, let alone be given any common name. Some have evolved complex or bizarre leaf shapes, unlike those of any other plant. Mosses and hepatics are distantly related. Collectively, they are called bryophytes. They seem to date back to the Carboniferous era, and beyond, and they differ fundamentally from every other plant and animal on earth, save some fungi, bacteria and algae. However, the difference is not easy to explain to a layman. People have three kinds of cells. There are male sperm cells, which can swim, and have one set of chromosomes, and there are passive female egg cells, also with one set of chromosomes. After they have fused, all other human cells, male or female, from the moment of conception onwards, have two set of chromosomes. That is the way the animal kingdom is organised, down to the humblest flatworm or jellyfish, and beyond. Flowering plants are organised in the same way, except that the male cells have lost their tails, and cannot swim. They have evolved into drought-rsistant pollen grains, which must be carried passively by wind or insects, to an unfertilized flower with female parts. Ferns and their relatives, such as horsetails, clubmosses, Selaginellas, and so on, are organised more like animals. They have male cells which contradict our ideas about the dfifferences between the two kingdoms. Their male cells have tails like animal sperm, and swim actively towards an unfertilised female cell, guided by chemical signals. When they fertilise one, a new plant begins to form, now with two sets of chromosomes. However the mature plant eventually produces single-celled spores, each with only one set of chromosomes, which float away, and germinate into something quite different.This something different, called a prothallus, looks like a small delicate leafless liverwort. It has a very simple structure, and only one set of chromosomes in each cell. It is this, not the mature plant, which eventually produces male and female organs. Fertilisation can only occur when the prothallus is wet, so that the male cells can swim through a film of water. The fertilised female cell now has a second set of chromosomes, and develops into an adult fern. A moss spore also germinates into something unlike the adult plant. The so-called protonema usually consists of filaments, strings of cells like those of some small alga. They branch and spread. From them, like the first fronds of a fertilised fern prothallus, the leafy shoots arise. However appearances are deceptive. No male of female cells have been produced, nothing has been fertilised, and the adult moss or hepatic still has ony one set of chromosomes in each cell. The fact that a moss appears to have roots, stems and leaves, like other plants, is a co-incidence of parallel evolution. Except for the prothallus of a fern, it has no analogies and no known relatives in the entire vegetable kingdom. Nobody has ever found a missing link, nor any other plant intermediate between a bryophyte and anything else. They are a unique and isolated group, though a large and successful one. The mature plant eventually produces male and female cells on tiny inflorescences. Acrocarps have them at the tips of the shoots, pleurocarps at the sides. Like flowering plants, some mosses produce both sexes on the same plant, or even on the same inflorescence. Some only produce inflorescences of one sex, and another distinct plant of the other sex must be nearby for fertilisation to occur. Some never seem to produce inflorescences capsules or spores at all, and are always sterile, only spreading vegetatively. Some mosses have the male cells surrounded by a rosette of modified leaves. In Polytrichum these are obvious, and often bight red, resembling small flowers. The male cells need a film of water to swim through. When one reaches a female cell and fuses with it, a new structure begins to form. Wrapped in a tiny sac, the new tissue, now with two sets of chromosomes in each cell, forms a stalk (a seta) and, at the top, a capsule, in which the next generation of spores will develop. In hepatics the stalk is thin, white, and delicate. It collapses and dies within days. The capsule is dark, and splits into four to release the spores. In all mosses except Sphagnum, the seta is tough, wiry and persistent. The capsule has an opening through which spores are shaken out, as if from a pepper pot.. The opening is usually fringed with a delicate set of teeth, produced in multiples of four, and called a peristome. This structure often helps to identify different genera and species, and defines their relationships. A moss capsule often has also a temporary lid, called a calyptra. The distinction between acrocarps (upright mosses) and pleurocarps (creeping mosses) is more than one of habit. Acrocarps have their seta and capsule at the end of the shoot, pleurocarps at the side. Liverwort capsules, before their stalk elongates, are usually wrapped in modified or enlarged leaves which form a “perianth”. In many, like Cephalozia, these leaves form a conspicuous translucent bag enclosing the young fruit. Sphagnum capsules are more like those of a liverwort than those of other mosses, being lifted on a soft white stem, and splitting into four when ripe. Otherwise there is no overlap between the two groups, nor any outward sign of a common ancestry. All this - and more - is in every university biology textbook, and in some school textbooks too. Even the most lucid explanation is bound to seem complicated. It is no wonder that many of those who first encounter mosses in botanical textbooks find them dull and complicated. Yet anyone who tries to grow mosses will appreciate what is happening better, if they understand a little about their life cycle. Mosses can be grown from spores, but outside a laboratory it is an uncertain process. What is more intriguing is that every part of the normal plant is interchangeable. Any part of a moss plant, so long as it contains a single healthy cell - a fragment of a leaf, or of protonema in soil, for instance - can produce new shoots, or new rhizoids, directly. Or it can produce new protonema. This may spread across the soil as a fine green film, and then form hundreds of new shoots. Slender rhizoids, or stout rhizomes, as in Polytrichum, may spread underground, and produce new shoots some distance from the parent plant. Furthermore, any soil in which an acrocarpous moss has been growing is likely to contain a few rhizoids. If a fragment of such soil is cultivated, the moss is likely to re-appear. Mosses are in fact incredibly flexible plants, able to re-appear or to colonise in the most unexpected ways. Sometimes the protonema is the most obvious part of the plant. If you look at a patch of freshly exposed soil, especially clay soil, in damp autumn weather, you may see small green stains, an inch or two across. Each of these may represent protonema from a single spore or fragment of some ephemeral moss. Presently a whole tuft, hundreds of stems, may appear, all from one spore. Growing tiny fragments or spores, a lucky grower may get the same result, but until identifiable leafy shoots arise, there is no way of knowing if the protonema is of the species it was intended to grow, Only the most careful of sterile cultures can be relied upon, not to produce something else instead. Moss protonema may look featureless in comparison with the mature leafy shoots, but has complexities of its own. There is often a distinction between green protonema, which photosynthesises, and brown protonema, which may grow down into the soil, and can lie dormant, awaiting another season. Some mosses make fragile erect protonemal branches which break off to spread the plant, or specialised underground cells which can lie dormant for years, before germinating when conditions are right. In recent years protonena has been the subject of many interesting observations and pieces of research. In many mosses, the protonema is scarcely visible, and only in the youngest plants, but there are some British mosses in which the protonema is the most noticeable part, and which I once had trouble in keeping on a long-term basis. On shaded banks of acid soil, especially vertical clay banks in hilly districts, an intensely deep green felt like growth of protonema can often be seen. From it spring the small stiff shoots of Pogonatum aloides, which resemble miniature Aloes, or plants of the related genus Polytrichum. Some shoots will often be found with flower-like male inflorescence. The large distinctive fruit is common and conspicuous. It is thus a fine plant for demonstrating the life cycle of mosses. It can be grown on damp acid clay, in deep shade, and shoots, leaves, or pieces of protonema put on fresh soil every few months. It has not been very vigorous in culture for me, and may have found greenhouse temperatures too high for comfort. A less common plant of deeply shaded acid rock clefts and cave entrances is Schistostega pennata. The leafy shoots are like those of a feeble Fissidens, but are so small, they are hardly likely to be noticed. Its unique glory is its protonema, which contains enlarged transparent cells, designed, as lenses, to focus the faint light of their dark habitat onto the speck of chlorophyll they contain. Like the lens in a cat’s eye, they also reflect light back, and someone looking at it in a dark cave, may see an eerie glow like green fire, shimmering against the dark rock or soil. I have kept Schistostega on acid sandy soil in enclosed plastic or glass containers (jamjars, etc.), in a dark cool corner of a greenhouse and even, for a time, on a bookshelf on an indoors landing. It is easily overrun by other mosses or hepatics, but fresh cultures, planted on with tweezers and a lens, can colonise fresh soil quite quickly. It grew fast in jamjars indoors, its flourescent green protonema reflecting back the faint light frown a light or window. Apart from this remarkable ability to spread by means of protonema, or to regenerate from tiny fragments, many mosses produce special small shoots, bulbils or gemmae, which are designed, like seeds, to fall off, to spread around, and to grow. Those of Bryum bicolor, B. rubens and B. subapiculatum were mentioned in chapter 5. Many other mosses, especially those of arable fields and disturbed ground, produce tubers. They are usually buried in the ground, like microscopic potatoes. In a related genus, Pohlia, there are several small species which make pale tufts on damp acid or neutral soil, woodland paths, and so on. A lens will often show tiny specialised shoots or bulbils of a variety of curious shapes, tucked among the upper leaves. These small plants are best grown on damp acid loam, in pots, or mounted, but they can appear as weeds among other cultivated mosses, in various soils and situations. Less obvious, except under a microscope, are the round or oval gemmae, growths often only one or two cells in size, which are produced by many small acrocarps. Sometimes they are clustered on the tips of the leaves, and can be seen through a lens. They give a brown fuzzy look to the leaftips of Ulota phyllantha and Orthotrichum lyellii, mosses which grow on trees in unpolluted areas. Advice on growing these comes later. Leaftip gemmae are common on many leafy liverworts, especially Lophozias. They make a pale, or green, or brown or even bright reddish powdery growth on the tips and edges of leaves, or on the tips of specialised stems, as on Calypogeia, mentioned earlier. There are two very distinctive mosses which are reasonably frequent in lowland Britain, and which have remarkable gemmae. Both grow on decaying wood, or on peaty banks in acid woodland. They are usually about 5 mm. tall. Aulocomnim androgynum makes little stalks with a tiny ball of powdery green gemmae at a the top. Tetraphis pellucida has little leafy cups at the top of the stem, containing gemmae, like the gemma cups of Marchantia, but much smaller. Both can be grown on peat, or better, on decaying wood, and prefer shade. Indeed, they will grow well in quite a dark corner of a greenhouse. They can survive drought, but will only flourish if they are not allowed to dry out too often. On wet rotting wood, the gemmae of Tetraphis grow in a strange way. They develop first into little leafless plants like small liverworts or fern prothalli, before putting up a normal leafy shoot. There is another very different Aulocomnium species, a striking large golden-green plant. Typically, it creeps among Sphagnum, and may be grown in the same way. Aulocomnium palustre, like A. androgynum, often makes elongated stems with clusters of gemmae at the tips. They get everywhere. It can be a vigorous weed in wet peaty cultures. It has even grown upside down in the grooves of my greenhouse roof, where condensation collected. These specially adapted gemmae and deciduous shoots are less common among pleurocarpous mosses (though Aulacomnium palustre looks and grows like a pleurocarp, it is not one). Growing plants from gemmae poses the same problem as growing them from spores or other small fragments. You start with something so small you cannot see it, or check its progress. It is likely to by washed away, dried up, or overwhelmed by something else, and you will never know what happened to it. Mounted cultures are far better in this respect. In a good light, and with a x20 lens, it is possible to keep track of single shoots, gemmae or small pieces of protonema, and weedy mosses and algae are less likely, less invasive, and more easily removed. Another useful technique for growing something very small is to make the cleanest possible culture on a pot of fresh soil. The soil surface can be sterilised by wetting it with bleach, then leaving it for a day or two, for the bleach to dissipate. The plant can then be added, and the whole pot wrapped in cling film. Keep it shaded, and when something green begins to spread, remove the cling film and turn a lens on it. If it doesn’t look like the plant you want, start again. If it does, discard the cling film, and water thoroughly, especially if algae are present. After a few weeks, algae get a hold anyway, however clean the culture to start with. They will eventually poison or overwhelm almost any mosses in an enclosed pot of soil. Soil which is sprayed with water reasonably often, and reasonably forcefully, will remain cleaner, as the algae are washed away, It certainly adds to the interest, to understand how mosses spread and propagate. However, growing them from gemmae, tubers or protonema, is usually less reliable that starting with a mature plant, or at least, with a plant that can be recognised. And as for spores... If you really want to do it the hard way, test tube cultures may be the only option |