Everand Logo

Welcome to Everand!

  • Discover millions of ebooks, audiobooks, and so much more with a free trial

    Only $9.99/month after trial. Cancel anytime.

    Fungi
    Fungi
    Fungi
    Ebook765 pages9 hours

    Fungi

    By Brian Spooner and Peter Roberts

    4/5

    ()

    Read preview

    About this ebook

    A comprehensive account of the natural history of fungi, from their lifestyle, habitats and ecology to their uses for humans. This edition is exclusive to newnaturalists.com

    How do we use fungi in medicine? How can we identify edible mushrooms? Brian Spooner and Peter Roberts are both widely respected experts in fungi from the Royal Botanic Gardens at Kew. In this highly authoritative guide they examine all aspects of fungi, from their lifestyle and habitats to their diverse reproductive strategies. New Naturalist Fungi covers all aspects of the subject including:

    • The biology and evolution of fungi
    • Fungi as agents of growth and decay
    • The relation of fungi to man, mammals and parasites
    • Their natural and man-made habitats

    Exploring the rich variety of mushrooms and toadstools found living in woodlands, grasslands, coastlines, rivers, and man-made habitats such as compost heaps, this New Naturalist volume is packed with information covering virtually every aspect of fungi. There is even a section on fungi in folklore and how humans have used fungi for medicinal purposes. With practical tips on collecting, preserving and identifying fungi, this is an ideal reference guide for enthusiastic amateurs and professionals alike.

    LanguageEnglish
    PublisherHarperCollins UK
    Release dateAug 19, 2010
    ISBN9780007406050
    Fungi
    Author

    Brian Spooner

    Brian Spooner is a mycologist at the Royal Botanic Gardens, Kew. He has participated in field expeditions and biodiversity projects in Malaysia and Australia. He regularly leads forays for the British Mycological Society. He is the author of several books and numerous research papers.

    Related to Fungi

    Titles in the series (99)

    View More
    View More

    Related ebooks

    Nature For You

    View More
    View More

    Related podcast episodes

    Related articles

    • Article

      Fascinating FUNGI

      Sep 24, 2020

      Fascinating FUNGI
      7 min read

    • Article

      A Touch Of Scarlet Fever

      Feb 5, 2020

      A Touch Of Scarlet Fever
      3 min read

    • Article

      Making A Mushroom Garden

      Feb 22, 2019

      Making A Mushroom Garden
      4 min read

    • Article

      What Lies Beneath

      Mar 1, 2022

      What Lies Beneath
      4 min read

    • Article

      How To Garden Like A Nonno

      Dec 5, 2021

      There is nothing better than having a nonno, and I should know: I had two of them. Nonnos are no-nonsense, hard-working and cheeky. They know how to fix things, how to make things, how to grow things, how to care for things. They basically know all t

      6 min read

    • Article

      Mini But Mighty: How Microbes Make The World

      Nov 15, 2019

      A pair of studies published this week expand our understanding of the ocean’s tiniest organisms, underscoring the vital role of the mighty microbe.

      6 min read

    • Article

      The Good Earth

      Oct 30, 2019

      The Good Earth
      10 min read

    • Article

      The Future Is Fungi

      Feb 24, 2022

      The Future Is Fungi
      11 min read

    • Article

      Gillian Burke

      Jun 2, 2022

      Gillian Burke
      2 min read

    • Article

      A Bug’s Menu

      Oct 24, 2018

      A Bug’s Menu
      5 min read

    • Article

      The Original World Wide Web

      Nov 17, 2023

      The Original World Wide Web
      7 min read

    • Article

      Edward O.wilson

      Jul 1, 2020

      Edward O.wilson
      5 min read

    • Article

      Is the Modern Mass Extinction Overrated?

      Oct 26, 2017

      After decades of researching the impact that humans are having on animal and plant species around the world, Chris Thomas has a simple message: Cheer up. Yes, we’ve wiped out woolly mammoths and ground sloths, and are finishing off black rhinos and S

      17 min read

    • Article

      The Superorganism That Created the Pandemic

      Mar 26, 2020

      I’ve spent years adventuring in exotic parts of the world seeking out wildlife—weeks in tents in remote wildernesses, nights uncomfortably holed up in hides in rainforests. I’ve drifted through mangroves on boats, even lodged in a tree-canopy camp. A

      5 min read

    • Article

      We Need Insects More Than They Need Us

      Jul 4, 2019

      The interconnection of the world is a wonder. Consider the United States Declaration of Independence, says Anne Sverdrup-Thygeson, a conservation biologist. It was written with the help of a wasp. In July, 1776, when Timothy Matlack, a clerk with sta

      11 min read

    • Article

      Great Unknowns Huge Questions Remain Unanswered About Life On Earth. We Asked Leading Scientists And Conservationists: What Is The One Thing You Would Like To Know About The Planet That Remains A Mystery?

      Dec 22, 2023

      Great Unknowns Huge Questions Remain Unanswered About Life On Earth. We Asked Leading Scientists And Conservationists: What Is The One Thing You Would Like To Know About The Planet That Remains A Mystery?
      3 min read

    • Article

      Noticing Microbial Worlds

      Oct 25, 2020

      Noticing Microbial Worlds
      7 min read

    • Article

      Humans And Fungi Have A Surprising Shared History

      Nov 6, 2023

      Have you ever wondered where mushrooms come from? Did you know that one of the largest organisms on Earth is a fungus? Are you curious about the rich history shared between humans and fungi? You might enjoy our book, Fungi, which delves into the scie

      3 min read

    • Article

      Reality Check

      Jul 6, 2023

      Reality Check
      4 min read

    • Article

      Our Earth Needs You!

      May 4, 2023

      Our Earth Needs You!
      2 min read

    Related categories

    Reviews for Fungi

    4/5

    4 ratings0 reviews

    What did you think?

    Tap to rate

    Review must be at least 10 words

      Book preview

      Fungi - Brian Spooner

      CHAPTER 1

      Neither Animals nor Plants

      ANIMAL, vegetable, or mineral? For centuries, this simple system of classification happily divided the natural world into three great, god-given categories. Fungi, if considered at all, were normally placed in the ‘vegetable’ category or occasionally (as ‘excrescences of the earth’) in amongst the minerals.

      We now know that fungi are neither plants nor animals, and are certainly not earthy outgrowths. But if not these, then what exactly are they? The question sounds simple, but proves in fact to be a highly complex one, with many aspects still not fully understood. The enormous diversity of the fungi, not just the larger and more obvious species, but the innumerable microfungi and ‘fungus-like’ organisms, presents an immense challenge in clarifying their interrelationships and defining their characters. Nevertheless, remarkable progress in recent years, due not least to the advent of molecular systematics, has painted a much clearer picture and allows a fuller answer to the question ‘What are fungi?’.

      In this first chapter, we consider this question and say something about the distinguishing characters of fungi, their classification, and main groups.

      Hyphae: the threads of fungal life

      Scoop up a handful of old, damp, woodland leaf litter and you will probably find that it is bound together with a cobweb-like mat of fungal strands. The same thing can be found in the compost of a mushroom bed or in a crumbling piece of rotten wood. Under a microscope, mushrooms themselves, the moulds on rotting food, and the hard brackets on a tree stump are all seen to be composed of these same fine strands. These are ‘hyphae’ (Fig. 1), the building blocks of all filamentous fungi. They are essentially hollow tubes, the living parts of which contain nuclei, mitochondria, and other organelles, just as do animal and plant cells. In most fungi, the hyphae are divided into compartments by cross-walls (septa), keeping the organelles separate in cell-like units, the septa themselves having microscopic pores, allowing movement of water and nutrients from one compartment to another.

      Fungi absorb nutrients through the walls of the hyphae, ‘feeding’ in much the same way as plant roots. All species can absorb small molecules such as amino acids and simple sugars, particularly glucose, but many produce digestive enzymes which can attack more complex substances such as cellulose and starch, breaking them down into simpler components. Wood-rotting fungi, for example, can break down cellulose and sometimes lignin, whilst others can break down keratin (found in hair and feathers), chitin (found in insects and other fungi), and various more surprising substances, including kerosene. This method of nutrition is the main reason why fungi are the principal agents of natural decay and nutrient recycling (Chapter Three).

      image 1

      FIG 1. Hyphae from the agaric Leucopaxillus giganteus showing septa (cross-walls) and swollen clamp connections (see also Fig. 4) which are typical of basidiomycetes (RBG Kew).

      image 2

      FIG 2. Mycelium of a corticioid fungus spreading over the underside of a log. The hyphae show a tendency to clump together, forming visible branches and fronds (S. Evans).

      Individual hyphae are microscopically small, typically around 5–20 µm wide (a micrometre (µm) or ‘micron’ is one millionth of a metre), but when branched and growing together they can easily be seen as a cobwebby, mould-like growth (Fig. 2). This is termed the ‘mycelium’ (or ‘spawn’ in cultivated mushrooms) and is how most filamentous fungi grow through a nutrient-rich substratum, be it rotten wood, dung, damp leaf litter, or a long-forgotten sandwich. Each hypha branches and grows from the tip, spreading indefinitely as long as there is a food source. Components needed to synthesise new walls are produced throughout the hypha and actively transported to the growing tip. Branching commonly occurs, usually behind a septum, by thinning of the hyphal wall and extension of a new growing tip. This method of growth can be extremely efficient in appropriate conditions, with growth rates in some fungi, such as the common ascomycete Neurospora crassa, as high as 6 mm per hour. This is one reason why moulds are such rapid and effective colonisers. It also explains why some fungi have become very large (the biggest living organisms on the planet, in fact) and also very old (potentially, perhaps even immortal).

      Fruitbodies: from mushrooms to moulds

      Hyphae become most visible when they combine to produce complex spore-bearing structures or ‘fruitbodies’. These fruitbodies include the mushrooms and toadstools, brackets, puffballs, truffles, cup fungi, morels, and so on, which most people think of as ‘fungi’.

      Examination of sections of any fruitbody under a microscope will demonstrate that it is almost entirely composed of hyphae. In fleshy species, like mushrooms, the hyphae are generally distinct and easily visible but in many fungi the hyphae are variously modified by being swollen, thick-walled, gelatinised, compacted, pigmented, ornamented, or any combination of these. From these structural hyphae, which comprise the bulk of any fruitbody, specialised spore-bearing hyphae arise, capable of releasing the spores by which the fungus reproduces and forms new colonies.

      An ordinary cultivated mushroom provides a familiar example. The fruitbodies arise from the mycelium in soil or compost, once it has reached a certain age and bulk. Their development is triggered by various factors, including temperature, humidity, aeration, nutrient availability, and the presence of physical constraints (many larger fungi fruit where mycelial growth is checked, often by compacted earth at the edge of a path). Though mushrooms famously grow in the dark, other fungi may need light to initiate fruiting. However, this can be astonishingly brief, an exposure of just 12 seconds being sufficient for Neurospora crassa. Blue light at the right intensity is required for this species, whilst others prefer near-ultraviolet light, or varying periods of light and darkness. The effects of light on fruitbody development can be quite complex, stimulating the development of some species but inhibiting others. In some cases, fruitbodies developed in dark conditions exhibit weird and monstrous forms (Chapter 13).

      Many species of dung-inhabiting fungi are ‘phototropic’, actively growing towards a light source in order to discharge their spores most efficiently into the air stream.

      The young mushroom fruitbody or ‘primordium’ initially resembles little more than a knot of hyphae, but quickly grows and differentiates below the soil surface. At the ‘button’ stage it is effectively fully formed and (if conditions, particularly humidity, are right) is ready to expand, breaking the surface and becoming visible as a fresh mushroom. It continues to expand and mature until the spores are released. This expansion phase, effectively using hydraulic pressure, is rapid and extremely powerful, generating a considerable force. Mushrooms developing below paving stones, for example, will readily lift the stones as they expand and mature. Buller (1931) showed that the delicate ink-cap toadstool Coprinus sterquilinus can raise a weight of over 200 grams during the development of its fruitbody, without breaking its stem. Spore production in the cultivated mushroom typically continues for several days (if left unpicked), after which the fruitbody collapses and rots away. A single mycelium will produce many such mushrooms, both simultaneously and in succession, during the fruiting season. In the wild state, further crops will be produced the following year, and so on indefinitely, as long as nutrients are available.

      The mushroom itself has three main parts: the stem (or ‘stipe’), which lifts the fertile part into the air; the cap (or ‘pileus’) which covers and supports the fruiting surface; and the gills (or ‘lamellae’), on which the spores are produced. In addition, protective membranes (or veils) are present in many mushroom and toadstool species. These may enclose the entire developing fruitbody (a universal veil) or cover just the developing gills (a partial veil). At maturity, these veils rupture and leave either a sac-like ‘volva’ at the base of the stem and scale-like remnants on the cap (universal veil), or a ring on the stem (partial veil) (Fig. 3).

      Though mushrooms and toadstools are ephemeral, lasting only for a few hours or at most for a few days, some of the wood-rotting bracket fungi have tough, long-lasting fruitbodies which allow a much longer period of spore release but represent a substantial investment for the fungus concerned. As a result, many brackets are perennial, some persisting for twenty years or more, producing a new spore-producing layer each year. It is often possible to count these, like tree rings, if the bracket is damaged or cut through vertically. The structural hyphae in such fruitbodies are unusually thick-walled (so-called ‘skeletal’ hyphae) and in the toughest fruitbodies are further strengthened by being interwoven with equally thick-walled ‘binding’ hyphae. The result may be a bracket that feels as hard and solid as the wood on which it is growing.

      image 3

      FIG 3. Features of a typical agaric fruitbody (Amanita species). The ring and volva are remnants of veils that rupture as the toadstool expands (P. Roberts).

      Most moulds, mildews, and other microfungi produce small, often microscopic fruitbodies, or have no specialised structures. Typically, a mould produces a felty colony of modified surface hyphae which produce asexual spores (or ‘conidia’) on specialised cells. These conidia, often produced in vast quantities, serve to colonise new and often ephemeral substrata.

      Sex and spores

      Sex, as we know it, is a very different process in the fungi. Indeed, some species, mainly moulds and yeasts, manage without it, and populations are essentially clones. In others, both sexual and asexual reproductive stages occur at different points in their life cycle, each stage producing a distinct and usually independent fruitbody, known as the ‘anamorph’ (asexual fruitbody) and ‘teleomorph’ (sexual fruitbody). In addition, a mechanism termed ‘heterokaryosis’, which also leads to genetic diversification, may occur in asexual stages. This follows fusion of different hyphae, which results in two or more genetically slightly different nuclear types in the same mycelium, providing some genetic mixing despite the lack of sex.

      In general, however, sexual reproduction is as important to fungi as to other organisms. Typically it involves the union of hyphae (or yeast cells) containing nuclei with a single set of chromosomes (i.e. haploid, with half the full complement), the resulting hypha (or cell) being then ‘dikaryotic’, containing nuclei of two different types. In basidiomycetes (the large group which includes mushrooms and toadstools) proliferation of dikaryotic hyphae usually occurs through the formation of ‘clamp connections’, unique structures found in no other group of fungi. After division of each nucleus, one nucleus migrates into a bulge in the wall of the hypha and, after formation of a septum, is transferred to the newly formed uninucleate adjacent cell, so maintaining the dikaryotic condition (Fig. 4). Sooner or later, the haploid nuclei in dikaryotic hyphae will fuse to produce a diploid nucleus with two sets of chromosomes. In due course, this nucleus undergoes ‘meiosis’, a division process which effectively restores the haploid condition, but combines in each resulting cell chromosomes from two different sources. Following meiosis, haploid spores are produced, allowing dispersal to occur (Fig. 5). A few species of fungi produce morphologically distinct reproductive cells, roughly the equivalent of sperm and ova, but since both can arise from the same parent fungus there is no real differentiation between ‘male’ and ‘female’.

      image 4

      FIG 4. How clamp connections are formed in basidiomycetes. Hyphae are typically dikaryotic (with two genetically distinct nuclei in each hyphal cell, represented by black and white dots). When the nuclei divide and new cells start to form, there is a danger that two of the same nuclei may enter the new cell. But the process of clamp formation, shown here in three very simplified stages, ensures that the dikaryotic condition is maintained (P. Roberts).

      Inbreeding within a population in general decreases its adaptive potential. In many fungi, populations are therefore self-sterile and can ‘mate’ only with adjacent populations. Such fungi are termed ‘heterothallic’. Others, in contrast, are self-fertile and these are known as ‘homothallic’. Heterothallism is due to the existence of ‘alleles’ (different types of a single gene) which effectively produce different strains of the same fungus, commonly referred to as ‘plus’ and ‘minus’. A plus strain cannot mate with another plus strain, but can do so with any minus strain. Such different mating types, morphologically indistinguishable, occur in the majority of fungi. The existence in many species of multiple alleles, present in different populations, can lead to highly complex situations with large numbers of mating types. The ink cap Coprinus cinereus, for example, has been shown to have at least 1,152 different mating types, whilst other fungi may have even more!

      image 5

      FIG 5. Meiosis in typical basidiomycetes. The young basidium is dikaryotic, containing two genetically distinct haploid nuclei. These fuse to form a single diploid nucleus which then undergoes meiosis, forming four new haploid nuclei. Each of the new nuclei then migrates into a developing haploid spore (P. Roberts).

      image 6

      FIG 6. A selection of fungal spores to give a flavour of the enormous diversity of size, shape, pigmentation, ornamentation and septation that they exhibit. Spores may be simple or multicellular, and many bear appendages or a mucilaginous coat, all adaptations to particular ecologies. Others may have complex coils and branches, as shown in Fig. 103 depicting spores of aquatic fungi (P. Roberts & B. Spooner).

      Most fungi produce some kind of spores, individually microscopic but varying enormously in size. The smallest, no more than about 2 or 3 µm across, are hardly larger than bacteria, whereas the largest may reach almost 500 µm (0.5 mm) in length (Fig. 6). In mushrooms and toadstools, spores are normally around 5–20 µm long, depending on species. They are typically produced in vast quantities, often in billions. To see them, take a mature mushroom, remove the stalk, place the cap on a piece of white paper or glass, cover with a glass to prevent drying out, and leave overnight. The result will be an attractive chocolate-brown spore deposit comprising several million spores (Fig. 7). Each spore is capable of germination, but clearly very, very few ever encounter precisely the right conditions to form a new mycelium and continue the species.

      image 7

      FIG 7. Spore deposit or ‘print’ of the commercial mushroom (Agaricus bisporus). As well as forming attractive patterns reflecting gill arrangement, spore deposits have scientific value in showing precise spore colour and in comprising fully mature spores (RBG Kew).

      A KINGDOM APART

      Fungi are clearly a very distinctive group of organisms, but just where do they fit into the grand scheme of things?

      All life on Earth can be classified into a number of separate, major units known as ‘kingdoms’, each representing an ancient lineage that has evolved into a multiplicity of modern species. Just how many kingdoms are required to encompass this multiplicity is, however, uncertain. The simplistic view recognised just two, ‘animals’ and ‘plants’, following classical beliefs established long before the foundation of modern systematics by Linnaeus in the mid 18th century. This comfortable tradition continued almost unchallenged for close on three centuries, and not until the latter part of the 20th century has it been radically reviewed and replaced. This change has largely reflected progress in the study of micro-organisms, involving ultrastructural and biochemical characters and especially the application of molecular systematics, advances which have finally shown that a two-kingdom system is hopelessly inadequate to encompass the huge diversity of life on Earth. A several-kingdom structure of life is now not in dispute.

      Although fungi, as well as protozoa and bacteria, had occasionally been considered separate kingdoms at various times since the 17th century, no consensus on this view was held until comparatively recently. Margulis & Schwartz (1982) were the first to propose the classification of living organisms into five kingdoms, following earlier suggestions by Whittaker (1969). More recently, a six kingdom system has been suggested (Cavalier-Smith, 1998), although it now seems that Woese et al. (1990) were correct in splitting one of these kingdoms (the Prokaryota or bacteria) into two, the Archaea and the Bacteria. Prokaryotes are single-celled structures, the most ancient of all organisms, with which life on Earth began. Their cells lack nuclei or other subcellular structures (organelles) such as mitochondria, and their DNA is dispersed. Prokaryotes probably evolved at least 4,000,000,000 years ago and were for an immense period of time the only life forms on the planet. Eventually, after at least two billion years of slow evolution, they gave rise to the more complex ‘eukaryotes’, organisms with sophisticated cells containing separate organelles. The most important of these are the ‘nucleus’, which governs the cell and in which the DNA is packaged, and the ‘mitochondria’, which provide energy.

      All life other than bacteria is eukaryotic, highly evolved and diversified over the last two billion years into five separate kingdoms. These are the plants (kingdom Plantae), the animals (kingdom Animalia), the true fungi (kingdom Fungi), and the less well-known kingdoms Chromista and Protozoawhich both contain some fungus-like organisms. Protozoa is probably the most ancient of the eukaryotic kingdoms and includes a total of thirteen ‘phyla’ (the next main unit (or taxon) below kingdom), a level which distinguishes human beings (phylum Chordata) from jellyfish (phylum Cnidaria). Animalia comprises 23 phyla, Plantae and Chromista each have five, and four phyla make up the Fungi. In this system, most of the organisms traditionally called ‘fungi’ belong within the kingdom Fungi, but some are placed within the Protozoa and Chromista. Although this seven-kingdom system is not yet fully accepted, it seems to be gaining favour as the current standard model. Nonetheless, significant changes are still being proposed and it seems likely that even the highest levels in the classification of life will remain in a state of flux for a long time to come.

      Defining the fungi

      Each of the seven kingdoms, as with all taxa, has its own unique features. In the old two-kingdom view of life, fungi were placed with plants mainly because, unlike animals, they do not move around. This is undeniably true, but is hardly a good scientific definition. The fungal mode of nutrition, for example, is quite different from that of plants. Like animals, they are ‘heterotrophs’, unable to make their own food and requiring organic carbon derived from plants or other organisms. Unlike animals, however, which ingest their food, fungi digest and absorb nutrients externally. Plants, in contrast, are ‘autotrophs’, making their food by photosynthesis, their cells containing chlorophyll and able to use sunlight to convert carbon dioxide into sugars. Fungi also differ structurally from plants, in particular lacking cellulose which is characteristic of plant cell walls. Instead, fungi are mainly composed of chitin, the same basic material that makes up insect exoskeletons.

      Recognition of a separate kingdom for fungi was a major advance, although it was soon evident that the kingdom was not yet homogeneous but included organisms placed there because of similarities in their mode of nutrition, now known to have arisen independently from a different ancestor. As long ago as 1864, de Bary had proposed that slime moulds were not fungi but actually protozoa, a conclusion which, because of the fungus-like nature of their fruitbodies, only recently received acceptance. Slime moulds (Myxomycota) are actually ‘phagotrophs’, ingesting bacteria and fungi by means of amoeboid stages, typical of protozoa. Again, the filamentous nature and mode of nutrition of the ‘actinomycetes’ placed them with the fungi until it was realised that they were actually prokaryotic and belonged instead with the bacteria. Their fungus-like characters were evolved quite independently, and the same has been found to apply to some other fungus-like organisms. As a result, definition of the ‘true fungi’ cannot be simply stated but relies on characters such as mode of nutrition, chemistry of the cell wall, biosynthetic pathways and ultrastructure of the mitochondria. The taxonomic value of this last character, first suggested in the 1960s, has now become firmly established (Cavalier-Smith, 2001). Mitochondrial cristae, essentially folds of the inner membrane of the mitochondrion, are flattened in Fungi but tubular in other groups, providing a major (but not the only) distinction between Fungi and other heterotrophs. On this basis, the kingdom can be technically defined as follows:

      "The Fungi comprise non-photosynthetic eukaryotes with an absorptive nutrition that do not have an amoeboid pseudopodial stage, and may occur as both single celled and multicelled organisms. The cell walls contain chitin and ß-glucans, and their mitochondria have flattened cristae."

      FROM MOULDS TO MUSHROOMS: A GUIDE TO THE MAJOR GROUPS

      The classification adopted for fungi in this book recognises the three kingdoms (Fungi, Chromista, and Protozoa) noted above and broadly follows that given in the most recent edition of the ‘Dictionary of the Fungi’ (Kirk et al., 2001), with some modifications based on recent findings. However, with continued rapid development of techniques such as molecular analysis it seems unlikely that the system suggested here will yet prove a stable one. Nevertheless, the following brief guide should help place the fungi discussed throughout this book into appropriate context.

      KINGDOM FUNGI: ASCOMYCOTA

      The Ascomycota, the largest of the fungal phyla, contains not only the more visible cup-fungi, morels and truffles, but also the ubiquitous and often microscopic flask fungi, most of the lichens, and many of the asexual yeasts and moulds. Ascomycetes occur worldwide, and exhibit an enormous range of life styles and forms. Currently, the phylum is divided into seven classes, 56 orders, and well over 200 families. Total species numbers are difficult to estimate, but it seems that at least 40,000 ascomycetes are known worldwide, with several times that number yet to be described. About 5,500 ascomycetes (excluding asexual stages likely to belong within this phylum) have been recorded from Britain, including around 1,800 lichenised species.

      Ascomycetes are characterised by the possession of ‘asci’, microscopic club-shaped cells in which sexual spores (‘ascospores’), are developed. Asci themselves are extremely diverse in structure and provide the basis for the current classification of these fungi (Fig. 8). In many species, including most of the larger ascomycetes, asci are simple structures which have a single, one-layer wall and are therefore referred to as ‘unitunicate’. However, many other ascomycetes have asci with complex wall structures involving more than one layer. These are termed ‘bitunicate’ but are themselves diverse in their microanatomy and method of functioning for spore discharge. Ascomycetes are also characterised by the structure of their hyphal walls which involve two layers of differing density to electrons. It is this character which can be used to determine the ascomycetous affinities of most asexual fungi in which the ascus stage is lacking.

      image 8

      FIG 8. Examples of different types of asci, the cells in which the spores of ascomycetes are produced. They exhibit immense diversity in shape, size, wall structure and method of spore release, providing a basis for classification of these fungi (B. Spooner).

      Two main forms of fruitbody provide convenient if artificial groupings for the bulk of species. These are the cup-fungi, or ‘discomycetes’, and the flask fungi, or ‘pyrenomycetes’. In addition, there are the ascomycetous yeasts together with the anamorphic stages of ascomycetes, usually known as ‘hyphomycetes’ and ‘coelomycetes’.

      Cup-fungi or discomycetes

      Cup-fungi are virtually cosmopolitan in distribution and occur in all habitat types. Although most are saprobes (living off dead matter), they also include mycorrhizal species (symbiotically associated with plant roots) as well as many parasites and pathogens. Some of the larger cup-fungi, particularly truffles and morels, are edible and sought after.

      The term ‘cup fungus’ refers only to a general design and has little taxonomic value in itself. The fruitbodies (known as ‘apothecia’) of most species take the form of miniature cups, goblets, or discs, with the spore-bearing layer on the inner surface. However, some have diverged markedly from this basic design, and form complex, compound structures, as in the honeycomb-like morels (Morchella species), or have become totally enclosed and chambered, as in the truffles and other subterranean species.

      Most apothecia are small, only a millimetre or so across and sometimes much smaller, but they often occur in swarms on rotting stems or leaves. Many are highly attractive, especially when examined with a lens, displaying a range of colours and often delicately ornamented with hair-like structures. Most of the smaller species have characteristic asci termed ‘inoperculate’ (lacking a lid) referring to their mode of spore discharge through an apical pore (as in the genus Bisporella, Fig. 9). They belong mainly to the order Helotiales and are the most numerous of the cup-fungi with perhaps 1,500 species known from Britain and 4,000 or so worldwide.

      image 9

      FIG 9. Bisporella citrina, one of the smaller inoperculate discomycetes, often found in swarms on dead wood and stems. The distinctive bright yellow fruitbodies are fairly common on rotten logs (B. Spooner).

      Fundamentally distinct from the Helotiales are the cup-fungi that belong to the Pezizales. These are distinguished by their asci being ‘operculate’, releasing their spores through an apical lid or ‘operculum’. Most Pezizales have easily visible fruitbodies often several centimetres across or more, and most of the larger cup fungi belong here. They include the striking orange-peel fungus Aleuria aurantia, the equally flamboyant scarlet elf-cups in the genus Sarcoscypha, and a range of variously coloured Otidea and Peziza species. More complex in form and among the largest of the Pezizales are the spring-fruiting morels (Morchella species) and autumn-fruiting saddle-fungi (Helvella species; Fig. 10). Though less numerous than the Helotiales, there are nevertheless over 300 species of Pezizales known in Britain and almost 1,200 worldwide. Closely related to them are the truffles (Tuber species) and others which have evolved underground fruitbodies adapted to their unique ecology and quite unlike typical discomycetes. They include some of the most sought after edible fungi.

      Disc-like fruitbodies are also produced by many lichens, these belonging mainly in the Lecanorales, distinguished not just by their mode of life but by the structure of their asci. This is the largest order of ascomycetes, comprising a huge range of forms currently divided into more than 40 families and including some 5,500 species worldwide, more than 1,000 of which occur in Britain.

      Although more than 11,000 cup-fungi (including lichenised species) have been described world-wide, they remain little known. New species are frequently encountered, and their ecology and life histories, physiology and chemistry are, for the most part, little-studied. Their bewildering diversity provides a seemingly endless challenge, even within the British Isles.

      image 10

      FIG 10. Helvella crispa, one of the larger operculate discomycetes which have become modified into a stalk and a saddle-shaped cap. This whitish species is common in woodlands (B. Spooner).

      Flask fungi or pyrenomycetes

      The second big group of ascomycetes has flask-shaped fruitbodies (‘perithecia’), fully enclosing the asci except, in most cases, for an apical pore (‘ostiole’) through which the spores are liberated. These fungi are even more diverse than the discomycetes, and are almost ubiquitous in their distribution. They include parasites as well as saprobes and symbionts, many of which are lichenised.

      The flask fungi have tiny fruitbodies, some less than a tenth of a millimetre wide and none exceeding about two millimetres across. Most are dark-walled, appearing black to the eye, although some, such as coral spot, Nectria cinnabarina, are bright red or orange. The fruitbodies are usually gregarious but often developed inside plant tissue and largely hidden from view with only the ostioles breaking the surface. Others, however, develop conspicuous and sometimes massive areas of sterile tissue in which numerous perithecia are immersed. Since this tissue, known as a ‘stroma’, is typically black, many of these flask fungi appear burnt or carbonised, hence the term ‘pyrenomycetes’ (literally ‘fire fungi’). Stromatic tissue varies greatly in structure and extent. At its simplest it merely comprises dark hyphae in the epidermal cells of the host, covering just a single perithecium, as in species of Anthostomella (Xylariaceae). In other cases, including most Diatrypaceae, it may blacken the host surface over extensive areas, or become crust-like or cushion-like with numerous embedded perithecia. Discrete, often massive, fruitbodies are formed in some pyrenomycetes, particularly in the Xylariaceae and Hypocreaceae. Amongst the largest of these are Daldinia species, called ‘cramp balls’ or ‘King Alfred’s cakes’, common in Britain, and species of Xylaria (Fig. 11), a genus which includes the familiar black and white candlesnuff fungus, Xylaria hypoxylon, and dead man’s fingers, X. polymorpha, on old stumps and logs. Cutting open one of these blackened ‘fingers’ reveals a core of whitish, sterile tissue with a multitude of tiny flask-shaped perithecia embedded in the surface layer.

      Ascus characters are again fundamental to the classification of pyrenomycetes and on this basis two major groups can be distinguished. The first includes the true flask fungi, ascomycetes with flask-like fruitbodies and unitunicate asci. These are currently divided into at least 12 orders and over 40 families, although their taxonomy remains inadequately understood.

      image 11

      FIG 11. Xylaria longipes, recently dubbed ‘dead moll’s fingers’, an ascomycete with large, stromatic fruitbodies. This species, distinguished by its slender, upright, unbranched fruitbodies, is quite common in Britain and occurs almost exclusively on dead roots and branches of sycamore (B. Spooner).

      Most have a well-defined hymenium of asci and paraphyses, with spores released by extension of the asci though the ostiole. In some, however, the fruitbody is a completely closed structure (known as a ‘cleistothecium’), and the asci break down so that forcible discharge of spores is lost. Most characteristic of such fungi are the Eurotiales, with asexual stages in the mould genera Aspergillus and Penicillium. Their fruitbodies are tiny, usually bright-coloured structures found on decaying plant matter. Other cleistothecial pyrenomycetes may be dark-coloured, such as species of Thielavia, often found on dung, and Preussia, sometimes found on old rope and rotting cloth. Also cleistothecial are the powdery mildews (Erysiphales; see Chapter Six), which are parasites of higher plants.

      Lichenised pyrenomycetes are numerous and involve several families. They may exhibit a wide range of thallus types though most are encrusting. The large genus Verrucaria, worldwide in distribution and well represented in Britain, is a typical example.

      Superficially similar to pyrenomycetes, though quite different in ascus structure, are the ‘loculoascomycetes’ or ‘false flask fungi’. They again are hugely diverse and encompass a vast array of species. They have structurally complex asci termed ‘bitunicate’ which commonly have two wall layers, the outermost being a rigid structure which ruptures at maturity and allows the inner wall to extend through the ostiolar region and forcibly discharge the spores. Fruitbodies of the loculoascomycetes (known as ‘pseudothecia’) are stromatic, usually comprising dark, often carbonised tissue, within which unwalled cavities or ‘locules’ are developed which contain the asci. They exhibit a great diversity of form including minute, flattened shield-shaped structures, elongated or upright fruitbodies shaped like the shell of a bivalve mollusc, and flask-like forms resembling those of true flask fungi. Some are even discoid, mimicking discomycetes in form. Patellaria, for example, has blackish, saucer-shaped fruitbodies very like those of Patellariopsis in the Helotiales. As with other ascomycetes, loculoascomycetes exhibit a wide range of habitats and life styles. Saprobes abound on all kinds of decaying vegetation, parasites are common, and lichenised species are frequent.

      Taphrina and Protomyces: gall-causing species

      Amongst the most conspicuous of the plant parasitic fungi are those which gall their hosts. This is characteristic of the Taphrinales (Taphrinomycetes), which lack proper fruitbodies but instead form asci either internally in the host tissue or in a palisade on the host surface. Their asexual states are yeast-like, formed by budding of ascospores in a similar way to that in the basidiomycete order Exobasidiales and some of the smuts. The Taphrinales, comprising only about 115 species worldwide, is unique in this respect and now considered ancestral to the whole phylum Ascomycota.

      Two families, Taphrinaceae, with a single genus Taphrina, and Protomycetaceae, with five small genera, are now referred to the Taphrinales. Some species of Taphrina induce conspicuous and often spectacular galls, including witches’ brooms and severe deformation and enlargement of leaves and fruit (Fig. 12). They infect many woody hosts, though about 25 species occur on ferns, a few, such as T. cornu-cervi on Arachniotes in the eastern tropics, causing remarkable antler-like outgrowths of the host leaves.

      image 12

      FIG 12. Taphrina deformans, the cause of ‘peach leaf curl’, a common but disfiguring disease of almond and peach in which the leaves are characteristically swollen and distorted, the galls being bright red at maturity and lined with the asci of the fungus (B. Spooner).

      Ascomycetous yeasts

      Yeasts are microscopic, usually single-celled fungi which reproduce asexually, typically by budding. They occur as stages in the life cycle of many different fungi, both ascomycetes and basidiomycetes, though in some cases the sexual stages are rarely formed or even lost entirely. Due to their simple form, their classification has presented many problems and species identification is still a difficult and specialist task involving chemical, physiological and developmental as well as morphological characters. However, yeasts are of immense economic importance, both as agents of fermentation in the production of food and drink (Chapter 17), and as human and animal pathogens (Chapter 15), and have therefore received detailed study. Around 700 species have been recognised worldwide, the majority being ascomycetous yeasts. Most belong to the ubiquitous order Saccharomycetales in which no fruitbodies are formed, but asci are produced either singly or in chains from vegetative cells from which they are often scarcely morphologically distinct. Asci may contain just a single spore, and commonly are evanescent, the wall breaking down to release the spores.

      The so-called ‘fission yeasts’, a tiny group including just two genera and five species, are also ascomycetes and comprise a distinct order Schizosaccharomycetales. In these, vegetative reproduction is by splitting or fission of the cells and there is no budding. The best known species, Schizosaccharomyces pombe, is an important fermentation yeast.

      Hyphomycetes and coelomycetes

      Hyphomycetes and coelomycetes are amongst the most commonly enountered microfungi. They are asexual, most of them being stages in the life cycles of ascomycetes, and are basically dispersive stages, usually able to reproduce themselves rapidly to colonise new hosts and take advantage of ephemeral substrates. In this, they are supremely successful, making their presence known even in the home by colonising everything from stale bread to damp wallpaper. Many produce vast quantities of conidia, which are easily dispersed and quick to colonise any suitable food source.

      The terms ‘hyphomycete’ and ‘coelomycete’ refer merely to the form of the fruiting structure and have no taxonomic value. In the former, conidia are developed on specialised hyphae (‘conidiophores’; Fig. 13) or sometimes from unspecialised mycelium and there is no well-defined structure on which these are borne. The fungi popularly known as ‘moulds’, including many ubiquitous species in the genera Penicillium, Aspergillus and Cladosporium, mainly belong here.

      image 13

      FIG 13. A range of conidiophores, the specialised hyphae on which conidia of asexual or anamorphic fungi are borne, showing some of the many different methods by which the conidia are developed (P.M. Kirk).

      Coelomycetes, in contrast, do produce a defined structure in which the conidia are formed. Commonly, these structures are flask shaped, resembling the fruitbodies of pyrenomycetes, and known as ‘pycnidia’. The common genera Phoma and Phomopsis, found on many plants and sometimes parasitic, are examples. As might be imagined, there is a vast array of forms produced by asexual fungi and in some cases the distinction between ‘hyphomycetes’ and ‘coelomycetes’ becomes blurred. These fungi, sometimes referred to as the ‘deuteromycetes’, ‘fungi imperfecti’, or ‘mitosporic fungi’, are anamorphs or asexual stages of ascomycetes, though many have no known teleomorphs and are accordingly known as ‘orphan anamorphs’. They may have lost the sexual stage in their life cycle or their appropriate teleomorph has not yet been discovered or recognised. This presents considerable difficulties in understanding numbers of fungal species. Although at least 16,000 species of hyphomycetes and coelomycetes have been described worldwide, the number of independent species which this represents is very uncertain.

      The genera of hyphomycetes and coelomycetes can be regarded only as artificial ‘form-genera’, belonging variously in a system which is defined by their sexual stages, and with no taxonomic value. Their classification has been based largely on the method of production and characteristics of their conidia, pigmentation of the hyphae, and the development and structure of the fruitbody. Amongst the hyphomycetes, many species have dark pigmentation in some part, and are known as ‘dematiaceous’. They are amongst the best known and most comprehensively studied of the hyphomycetes, in contrast to the numerous hyaline or unpigmented species many of which are still little known.

      KINGDOM FUNGI: BASIDIOMYCOTA

      The phylum Basidiomycota contains most of the familiar larger fungi, including mushrooms and toadstools, bracket fungi, and puffballs, as well as the rusts, the smuts, and much else besides. All produce their sexual spores externally on modified hyphae called ‘basidia’, the defining characteristic of the phylum (Fig. 14). The phylum itself is now divided into three classes – the Basidiomycetes, Urediniomycetes, and Ustilaginomycetes – based mainly on molecular and ultrastructure studies. The last two of these classes contain all the rusts and smuts (once lumped together as ‘teliomycetes’), together with some related plant parasites and a few of the jelly fungi. The Basidiomycetes contain the rest, including all the larger and more conspicuous members of the phylum.

      image 14

      FIG 14. Examples of different basidia: a) auricularioid (tubular with lateral septa), possibly the most ancient basidial form, found in many Urediniomycetes; b) tremelloid (ellipsoid with longitudinal or diagonal septa), typical of the Tremellales; c) tulasnelloid (with swollen sterigmata or epibasidia, septate at the base), characteristic of the Tulasnellales; d) holobasidioid (aseptate), typical of agarics and most basidiomycetes (P. Roberts).

      Approximately 30,000 basidiomycete species are known worldwide, with many more yet to be described. Some 3,600 have been recorded to date from the British Isles.

      Mushrooms and toadstools

      Mention the word ‘fungi’ to most people, and this is the group that first comes to mind. The old taxonomists placed all mushrooms and toadstools (including boletes) in the order Agaricales and referred to them as ‘agarics’. This is still the preferred scientific term for fungi producing agaricoid (mushroom-shaped) fruitbodies, most of which are ephemeral structures seldom lasting more than a few days (Fig. 15). Typically, these fruitbodies have gills (lamellae) on which the spores are produced although in most Boletales there are tubes instead.

      There is no real distinction between a ‘mushroom’ and a ‘toadstool’. Historically, vernacular usage in England has considered edible species to be mushrooms (as in field mushrooms, horse mushrooms, parasol mushrooms, St George’s mushrooms, etc.) and poisonous species (everything else, according to English belief) to be toadstools, though in a sense mushrooms are just edible toadstools. Amongst mycologists, the word ‘mushroom’ is often restricted to species of Agaricus (which includes the cultivated mushroom, A. bisporus, and the field mushroom, A. campestris).

      The classification of agarics into orders and families is still unsettled. The classical division, between those with white spores and those with dark or coloured spores, is still a useful starting point for practical identification, but taxonomically far too simple. Three major orders are now recognised: the Agaricales, where most species belong, the Boletales, and the Russulales. The last, which includes the important ectomycorrhizal genera Russula and Lactarius, are quite distinct and have long been recognised as forming a separate evolutionary line. Their hyphal structure often produces large cells which generally impart a fragile, often crumbly, consistency to the fruitbodies. However, it should be emphasised that many non-agaricoid forms are also now placed within these three orders. Furthermore, not all fungi with gills belong with the agarics! Some bracket fungi, such as Lenzites betulina, have gills, and typical agaricoid forms produced, for example, by Panus and Lentinus species, are more closely related to bracket fungi than to agarics.

      image 15

      FIG 15. Phaeolepiota aurea, a typical agaric. Fruitbody development shows cap, gills, and ringed stem. The ring is formed from the partial veil, a membrane which covers and protects the gills during development (B. Spooner).

      Worth noting in the context of Agaricales are the so-called ‘secotioid’ fungi. In these, the caps remain closed and never expand. Gills are formed and produce spores, but the caps, instead of opening like a normal toadstool, fragment like distintegrating puffballs to release the spores. Although no secotioid fungi occur in Britain, several species are known from southern Europe, and many more in North America and Australia. Their unusual form conserves moisture and many, notably the Mediterranean Montagnea arenaria and the widespread Podaxis pistillaris, are fungi of deserts or arid areas. Further modifications of such forms also occur, so that one can find a series of species running from normal agarics, to secotioid agarics, to those that resemble puffballs or truffles. Indeed, it is now believed that most of the basidiomycetous false truffles are more closely related to their respective agaric ancestors than they are to each other. Hydnangium carneum, for example, a pinkish false truffle not uncommon in Britain with Eucalyptus, is closely related to the agaric genus Laccaria and has similar spiny spores. Zelleromyces species, with a single species (Z. stephensii) in Britain, have spores similar to Lactarius species and are related (they even exude a milky latex when broken). More recently and more surprisingly, DNA evidence is strongly suggesting that ordinary puffballs (Lycoperdon species) belong in the same family as mushrooms (Agaricus species), though morphologically they could hardly appear more different.

      Ecologically, most agarics are either saprotrophs or ectomycorrhizal associates, though a few are parasites of plants or other fungi. The saprotrophs include many common grassland species (Chapter Eight), leaf and litter-rotting species (Chapters Three and Nine), and some specialist dung and firesite species (Chapter 13). Ectomycorrhizal toadstools associate with the roots of living plants, mainly forest trees, and include boletes, amanitas, russulas, and other familiar woodland fungi (Chapters Four and Nine). The plant parasites include such notorious species as honey fungus (the Armillaria mellea group), whilst among the parasites of other fungi are the piggy-back toadstools (Asterophora species) and the rare and peculiar Squamanita species (Chapter Six). Altogether, some 2,200 agaric species have been recorded from Britain.

      ‘Gasteromycetes’: puffballs, stinkhorns, and their allies

      ‘Gasteromycetes’ (literally ‘stomach fungi’) is the old collective name for a diverse range of fungi whose spores are typically produced and mature inside their fruitbodies. They are more appropriately referred to as the ‘gasteroid fungi’. They include the puffballs, earthstars, earthballs, bird’s-nest fungi, stinkhorns, and false truffles, and over 100 species occur in the British Isles.

      Four main types of gasteroid fungi can be distinguished: 1) the phalloids, exemplified by our common stinkhorn (Phallus impudicus); 2) the puffballs and allied species; 3) the bird’s-nest fungi; and 4) the false truffles. Phalloids produce gelatinous, egg-like fruitbodies which break and expand rapidly at maturity into upright, branched or cage-like structures on which spores are formed in a sticky and usually foul-smelling mass known as the ‘gleba’. These spores are dispersed by insects attracted by the smell. The phalloids are almost all bizarre-looking fungi, and include some particularly unusual and brightly coloured species in genera such as Aseroë and Clathrus (Chapter Seven). The more commonplace puffball-like fungi produce fruitbodies in which the spores at maturity form a powdery mass dispersed on the wind. The bird’s-nest fungi (Nidulariales) have spores which are formed in small, egg-like structures in cup- or goblet-shaped fruitbodies and are dispersed by rain-splash. The false truffles are subterranean basidiomycetes, superficially resembling the true truffles, some of which are quite common in the British Isles.

      Unfortunately, these main forms have little taxonomic value and, based mainly on molecular evidence, the gasteroid fungi are now placed in a variety of different groups, some of which may be rather surprising. For example, puffballs, until recently referred to their own order, Lycoperdales, are now thought to be atypical members of the Agaricales. On the other hand, the superficially similar earthstars (Geastrum species) are now placed in the order Phallales, whilst Astraeus hygrometricus, which looks like an earthstar, is placed in the Boletales, along with the earthballs (Scleroderma species). The bird’s-nest fungi have their own family within the Agaricales, as do the stilt-puffballs (Battarraea and Tulostoma). The false truffles are variously dispersed, mostly within the Agaricales, Boletales, Phallales, and Russulales.

      Many of the false truffles are ectomycorrhizal, as are earthballs and the dyeball Pisolithus arrhizus. Most other gasteromycetes are saprotrophs in grass and woodlands, Sphaerobolus stellatus and Cyathus stercoreus being most frequent on dung. None appears to be parasitic.

      Aphyllophoroid fungi: brackets, corals, and hedgehogs

      Having divided off the agarics and the gasteromycetes, the old taxonomists were left with a large and confusing assortment of differently shaped basidiomycetes which they placed in a catch-all order ‘aphyllophorales’ (meaning ‘non-gilled’ fungi). Needless to say, this is an entirely artificial and diverse assemblage, including all the bracket fungi, the corticioid or patch-forming fungi, the club and coral fungi, the hedgehog fungi, and more besides.

      The bracket fungi, or polypores, are a diverse group of primarily wood-rotting species in which the hymenium is poroid or sponge-like, or gill-like in a few species. The fruitbodies are typically produced on dead trunks and stumps, on fallen wood, occasionally on living trees, or on dead, buried roots. Species growing on exposed wood are often highly adapted, having evolved specialist ways of resisting desiccation. Many produce tough, perennial fruitbodies such as the big, woody-hard Ganoderma brackets often seen on stumps or at the base of old but still living trees, which can last twenty years or more. The southern species, Rigidoporus ulmarius, typically found on old elms, produces some of the largest of all known fungal fruitbodies, with brackets up to two metres across. Altogether, around 100 species of polypores occur in Britain,

      Enjoying the preview?
      Page 1 of 1