TRAINING SCHOOL
FPS COST Action FP1401 GLOBAL WARMING
FUNGAL TAXONOMY AND FUNGAL IDENTIFICATION USING TRADITIONAL TECHNIQUES
TAXONOMY AND IDENTIFICATION OF ASCOMYCETES
Tutor: David Minter
CABI, Bakeham Lane, Egham, Surrey, TW20 9TY, UK
Definition of ascomycetes and brief description of their main structures. The Ascomycota (informally known as the
ascomycetes) is the largest Division of Kingdom Fungi, with well over 60,000 species already described worldwide. Like
all fungi, they spread by a branching network (known as a mycelium) composed of usually cylindrical cells called hyphae
(singular hypha). Ascomycetes are characterised by producing sexual state spores (ascospores) in a special sac called an
ascus (plural asci). In most species, these sacs are formed on or in a larger structure called an ascoma (plural ascomata)
where they usually form a clearly defined layer called the hymenium. Within that layer there are often additional
modified cells which may function as packing material, and they are called paraphyses (singular paraphysis). Many of
them also produce other asexual spores called conidia (singular conidium). Conidia are produced from more or less
modified hyphae without involvement of an ascus. Those modified hyphae are called conidiogenous cells.
Conidiogenous cells themselves are sometimes carried on distinctly modified groups of hyphae called conidiophores.
Collectively, all of these (i.e. conidia, conidiogenous cells and conidiophores) may be formed in or on their own larger
structures called conidiomata (singular conidioma), analogous to but separate from ascomata. In some ascomycetes,
individual ascomata and/or conidiomata may be immersed in a larger often black and brittle expanse of mycelium called
a stroma (plural stromata). In addition, there are some fungi which are clearly ascomycetes on the basis of many other
features, but which do not produce ascospores (perhaps they have lost the ability to do so during evolution). Many of
these produce only conidia.
Sources of nutrition. About half of all ascomycete species form mutualistic relationships with photosynthetic algae or
bacteria and exist as lichens. These will not be considered in detail in the present workshop. Most of the remainder derive
their nutrition from plant material, as mutualists, parasites or saprobes. A few derive their nutrition from animal, fungal
or other substrata.
Asci. Special sac cells in which, following genetic recombination, the sexual state spores (ascospores) are formed. Asci
usually contain eight ascospores (the result of one meiosis followed by one mitotsis), but the number may vary from one
to several hundred. In some species asci containing different numbers of spores can be found within a single ascoma.
Asci may have one to several cell walls, and in many species asci have specially modified apical opening mechanisms to
release the ascospores. These are generally very important for classifying ascomycetes.
Ascomata. The “fruitbody” which contains asci. Ascomata are usually black or dark brown, but may also be brightly
coloured. There are three main types. Cup-shaped ascomata (sometimes called “apothecia”, open widely to reveal the
hymenium, so that ascospores can easily be shot into the air. Flask-shaped ascomata (sometimes called “perithecia”),
keep their hymenium enclosed, but produce a small apical pore (also known as an ostiole) through which ascospores can
be released, either shot into the air or for invertebrate or water dispersal. Totally enclosed ascomata (sometimes called
“cleistothecia”), have no opening, but rely on external factors for ascospore dispersal, for example by animals eating the
ascoma and distributing ascospores in their dung. These three types are of limited taxonomic value as they express a
spore distribution strategy which is likely to have evolved many times.
Ascospores. These are the sexual state spores. Because they are formed entirely within the ascus, they do not have the
scars seen on conidia where the conidia were attached to the cell which produced them. Ascospores are varied in shape
and size, and may consist of one to many cells. They may have ornamentation, including germ slits and germ pores.
Their shape can sometimes provide clues about the asci in which they were formed.
Conidia. These are the asexual state spores. In most it is possible to see evidence of how they were attached to the
conidiogenous cells which produced them. They are more varied in shape and size than ascospores, and have a similar
range of ornamentation. In some the shape provides valuable clues about the habitat occupied by the fungus: for example,
many star-shaped conidia are associated with freshwater habitats.
Conidiogenous cells. These are more or less modified hyphae which produce conidia. The order of events as each
conidium is produced provides much valuable information for identification. In particular the ways in which conidia are
initiated, delimited, and released, and the ways in which the conidiogenous cells then proliferate to produce subsequent
conidia, are all very important taxonomic characters. Interpreting them is, however, difficult.
Conidiomata. These are similar to ascomata in size and shape, but contain conidiophores, conidiogenous cells and
conidia.
Conidiophores. Specially modified hyphae which carry the conidiogenous cells, often with the function of raising them
above the substratum to facilitate air dispersal of the conidia.
Hyphae. The basic building blocks of the fungi. Branched, cylindrical cells forming a network (mycelium) for
assimilating nutrition, and after modification to a greater or lesser extent also forming the ascomata and conidiomata and
their contents.
Mycelium. A collective noun for a network of hyphae.
Paraphyses. Special cells lodged between asci within an ascoma.
Stromata. Black and brittle mycelium forming a tough structure which protects, supports or encloses ascomata and
conidiomata.
Internet resources for identification
There is a huge amount on the Internet. If you know the identity of the organism on which your fungus has been found,
go to the websites which provide lists of associations between fungi and other organisms. At present, Cybertruffle is
probably the best.
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Biodiversity Heritage Library [www.biodiversitylibrary.org]. A wonderful resource for older taxonomic literature,
but mainly valuable if you know what you are looking for.
Checklist of Fungi of the British Isles [www.fieldmycology.net/GBCHKLST/gbchklst.asp]. A significant database for
the UK, listing where, when and on what fungi have been observed. Mainly valuable if you are interested in a
particular species.
Cybertruffle: Cyberliber [www.cybertruffle.org.uk/cyberliber]. A digital on-line library specialized for mycological
literature and open access.
Cybertruffle: Cybernome and Robigalia [www.cybertruffle.org.uk/cybernome/eng]. Particularly valuable in
providing lists of fungi associated with a given organism. Global in scope, with information about where, when and
on what fungi and their associated organisms have been observed. Also functions in other languages including
Arabic, Chinese, French, German, Polish, Portuguese, Russian, Spanish and Ukrainian.
Fungus Conservation Trust CATE2 Database [www.abfg.org]. Provides lists of fungi associated with a given
organism for the UK, with information about where, when and on what fungi and their associated organisms have
been observed.
GBIF [www.gbif.org]. A huge global database with many records of where and when fungi have been observed, but
with no information about associated organisms.
Google [www.google.co.uk]. Also Google Images and Google Scholar. Yandex, the Russian equivalent of Google,
and Baidu, the Chinese equivalent of Google can also be valuable sources of information.
Landcare Research New Zealand [http://nzfungi2.landcareresearch.co.nz]. Provides lists of fungi associated with a
given organism particularly for New Zealand, with information about where, when and on what fungi and their
associated organisms have been observed.
Mycoportal [www.mycoportal.org]. A coalition of North American fungal reference collections, providing a huge
amount of information about when, where and on what fungi occur, but not easy to search.
USDA Fungal Databases [http://nt.ars-grin.gov/fungaldatabases]. An enormous database for fungi on plants and
plant products, with emphasis on the USA, and providing a huge amount of information about when, where and on
what fungi occur, but not easy to search.
Wikipedia [https://en.wikipedia.org]. Often maligned, but enormously useful!
Book resources for identification
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Ainsworth, G.C., Sparrow, F.K. & Sussman, A.S. The Fungi. An Advanced Treatise. Vol. 4A. The Ascomycetes and
Fungi Imperfecti. Academic Press (1973).
Breitenbach, J. & Kränzlin, F. Champignons de Suisse. Tome 1. Les Ascomycètes. Edition Mykologia (1981).
Cannon, P.F. & Kirk, P.M. Fungal Families of the World. CABI (2007).
Dennis, R.W.G. British Ascomycetes. Cramer (1978).
Ellis, M.B. Dematiaceous Hyphomycetes. CABI (1971).
Ellis, M.B. More Dematiaceous Hyphomycetes. CABI (1976).
Ellis, M.B. & Ellis, J.P. Microfungi on Land Plants. Croom Helm (1986).
Kirk, P.M., Cannon, P.F., Minter, D.W. & Stalpers, J. Dictionary of the Fungi. 10th edition, CABI (2008).
Seifert, K., Morgan-Jones, G., Gams, W. & Kendrick, W.B. The Genera of Hyphomycetes. Centraalbureau voor
Schimmelcultures (2011).
Sutton, B.C. The Coelomycetes. CABI (1980).
Plate 1. Ascomata (various magnifications). A. Brightly coloured cup-shaped ascomata (Lachnellula sp.). B. Vertical section of part of a cup-shaped
ascoma showing the hymenium as an upper layer (Mollisia sp.). C. Cup-shaped ascoma embedded in a dead pine needle, splitting apart the covering
layer - individual asci can be seen within (Lophodermium pinastri). D. Vertical section of Lophodermium pinastri - the hymenium is the pale layer in
the centre, protected by the darkened upper and lower walls of the ascoma. E. Black and brittle stroma on surface of wood, with flask shaped ascomata
so deeply embedded that only the ostioles can be seen (Nummularia sp.). F. Vertical section of a black and brittle stroma with flask-shaped ascomata
embedded in it (Nummularia sp.). G. Flask-shaped ascomata deeply embedded in a dead pine needle - only the ostioles can be seen (Anthostomella
formosa). H. A stalked stroma with swollen apex in which flask-shaped ascomata are embedded (Cordyceps sp.). I. Vertical section through a stalked
stroma, showing flask-shaped ascomata embedded in the swollen apex (Cordyceps sp.). J. Ascospores oozing from an apical ostiole at the end of a long
neck on a flask-shaped ascoma (Ceratocystis sp.). K. Multiple cup-shaped ascomata united as a single structure on a stalk (Morchella sp.). L. A totally
enclosed ascoma - the lower specimen shows the interior - a convoluted hymenium (Tuber melanosporum).
Plate 2. Asci, ascospores and paraphyses (various magnifications). A. Asci of Pleospora herbarum, showing two-layered ascus walls, each ascus
containing 8 brown multicellular ascospores. B. Ascus of Valsa sp., showing apical apparatus and containing sausage-shaped ascospores. Asci of this
species detach easily from the hymenium. C. Three asci of Mollisia sp. at different stages of development, the oldest containing 8 ascospores, with
adjacent paraphyses. D. Scanning electron micrograph of ascus apex of Elytroderma torres-juanii, showing thinner apical area with ascospore beneath.
E. Thin-walled asci of Corynelia tropica. F. Ascus of Sporormia sp. - the outer ascus wall has broken, and the inner wall has extended. G. Asci of
Nitschkia brommeana, each containing more than 100 ascospores arranged in a herring-bone pattern. H. Very thin-walled asci of Chaetomium
globosum, with adjacent paraphyses. I. The apices of three asci of Nummularia sp., mounted in iodine with a blue reaction indicating starch in the
apical apparatus. J. Asci of Elaphomyces sp., showing how different numbers of ascospores can be seen in asci from the same ascoma. K. Ascus,
ascospores and paraphyses of Lophodermium baculiferum. L. Asci, ascospores and paraphyses of Geopora sp. - note open lid at apex of discharged
ascus on left. M. Asci of Cordyceps sp., showing thickened apices and long thin ascospores each composed of many cells. N. Ascus of Pleospora
herbarum (compare with A), showing broken outer wall, extended inner wall, and broken off lid.
Plate 3. Conidiophores, conidiogenous cells and conidia (various magnifications). A. Conidiophores, conidiogenous cells and conidia of Thysanophora
glauco-albida on the surface of a dead pine needle. B. Conidiophores, conidiogenous cells and conidia of Thysanophora glauco-albida under the
microscope - note how conidia are produced in unbranched chains with the youngest at the base from conidiogenous cells which have thickened walls
around the fertile point. C. Conidiogenous cells and conidia of Phaeostalagmus peregrinus showing conidia produced from a fertile point inside a
protective “collarette”. D. Conidiophore and conidiogenous cell of Endophragmiella pinicola with a single conidium at the apex. E. Conidiophore of
Endophragmiella pinicola showing proliferation of the conidiogenous cell through the remnants of the wall of an earlier conidium. F. Conidiogenous
cell of Ramichloridium pini showing secessional scars, but no attached conidia. G. Single conidium of Ramichloridium pini with secessional scar
matching those shown in F. H. Conidiophore, conidiogenous cell and conidia of Oedocephalum sp., a species which produces many conidia
simultaneously from different points on a single conidiogenous cell. I. Colonies of Polyscytalum fecundissimum on a dead pine cone. J. Conidiogenous
cells and conidia of Polyscytalum fecundissimum - conidia are produced in branched chains with the youngest at the apex. K. Conidiophore and
conidium of Slimacomyces monosporus. L & M. Seceded conidia of Slimacomyces monosporus - secession is by random breakage of the conidiophore,
so some seceded conidia have longer stalks than others. N. Conidiogenous cells and conidia of Lophodermium baculiferum showing characteristic
“rabbits ears” formed by two conidia produced sequentially but close together in time.