Unit 1 Classification of Fungi

Dr. Deepthi B V
DoS in Microbiology, UoM
 Taxonomic problems associated with variation in fungi
1. Morphological similarities/differences:
• Unicellular and multicellular
• Unicellular- dimorphic
• Multicellular – thallus organization
• Coenocytic or septate / branched or unbranched
• Types of septa/ multi-septate
• Hyphal structures and their modifications – prosenchyma, pseudoparenchyma, rhizomorphs, sclerotia, appressorium,
haustoria, stroma, snares (hyphal traps)
• Reproduction/ reproductive structures
• Asexual – fragmentation, fission, budding, conidiophores, sporangiophores
• Asexual spores – types, septate, chains/single, shapes, ornamentation, arrangement etc
• Sexual reproduction types
2. Cryptic species – morphologically (phenotypically) similar but genetically (phylogenetically) different. Ex: A. fumigatus, A.
lentulus, A. udagawae.
3. Lack of universal genetic markers– ITS regions, IGS region, 18S rRNA, 28S rRNA (D1/D2), 5.8S rRNA (LSU & SSU of
rRNA), PKS etc 2
 Synchitrium

Plasmodium – amoeboid mass

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 Taxonomic problems associated with variation in fungi
4. Monophyly, polyphyly and Paraphyly:
• Monophyletic groups are those that include all descendants of a common ancestor (basis of taxonomy and evolution)
• Paraphyletic groups include some, but not all descendants of a common ancestor
• Polyphyletic groups are made up of organisms that have converged on a similar characteristic but do not share a common
ancestor.
5. Incomplete fossil record – sparse and incomplete, making it challenging to trace the history and origin of different fungal
groups
6. Limited culturing and identification techniques – difficult to study their morphology, physiology and reproductive structures;
environmental DNA sequencing has resulted in vast diversity of unculturable fungi that remain poorly classified.
7. Evolutionary convergence – unrelated fungal lineages evolve similar traits independently complicating the use of
morphological features for classification and leading to misinterpretation of their evolutionary relationships.
8. Nomenclature issues – reclassified, split, merged based on new information; the dual nomenclature system, where fungi were
sometimes named separately for their sexual (teleomorph) and asexual (anamorph) states, led to taxonomic complications – ‘One
fungus=One Name’ system
9. Horizontal gene transfer complicates phylogenetic analysis – presence of genes not inherited from a common ancestor –
leading to incorrect placement of species in taxonomic hierarchy. 8
 Classification of Fungi
• The classification of fungi is important for understanding diversity, phylogenetic relationships, ecological functions, and facilitating
identification.
• Initially, the division of mycota, or fungi and molds, includes the true slime molds (Myxomycetes), the lower fungi (Phycomycetes), and
the higher fungi (Eumycetes).
• The nomenclature is binomial, with a generic and a specific name (eg: Aspergillus niger).
• International Code of Botanical Nomenclature – Committee for fungi – effective publication, valid publication, typification, legitimacy and
priority.
• Species are collected in genera,
genera in families (suffix –aceae),
‘mycota’
families in orders (suffix-ales),
‘mycotina’
orders in classes (suffix-mycetes),
and classes in phylum/division (suffix – mycota) (sub phylum/division – mycotina) ‘mycetes’

• Major criteria used for classification: Morphological features ‘ales’

Anatomical characters (ultrastructural characteristics) ‘aceae’

Nutrition and physiology

Cell wall composition
Molecular methods
Classification of fungi

• Kingdom - Plantae; SubKingdom – Cryptogamae; Division – Thallophyta

• Fungal physiology & cell wall composition was different from both plants and animals – Ernst Haeckel (1866) – 3rd Kingdom - Protista
• Classification of fungi by Pier Andres Saccardo (1866) – fungi into 4 classes – Phycomycetes, Ascomycetes, Basidiomycetes and
Deuteromycetes.
• G.W. Martin (1961) - Contributed keys to the families of Fungi
• Classification of fungi by C.J. Alexopoulos (1962) – division Mycota
2 subdivisions – Myxomycotina (plasmodial forms)– single class – Myxomycetes
Eumycotina – (true fungi) 9 classes – Chytridiomycetes, Hypochytridiomycetes, Oomycetes, Plasmodiophoromycetes,
Zygomycetes, Trichomycetes, Ascomycetes, Basidiomycetes and Deuteromycetes.
• R H Whittaker (1969) – Five Kingdom Classification – Monera, Protista, Fungi, Plantae and Animalia.
• Classification of fungi by Ainsworth G.C (1973) – basis for all further classifications – Kingdom Fungi (Myceteae); 2 divisions –
Myxomycota (plasmodial forms) and Eumycota (non-plasmodial forms).
• Classification of fungi by C.J. Alexopoulos and C.W. Mims (1979) – Modified classification of Ainsworth
Superkingdom – Eukaryota; Kingdom – Myceteae; 3 division – Gymnomycota, Mastigomycota and Amastigomycota
• Classification of fungi based on the 10th Edn. of Dictionary of the Fungi by P.M. Kirk, P.F. Cannon, D.W. Minter and J.A. Staplers, 2008.
Monophyletic concept – 3 Kingdoms – Fungi, Chromista/Stramenopila and Protozoa
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Only for reference – not
in the syllabus

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Important and a part of
the syllabus
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 Classification of fungi

System Proposed by Constantine John Alexopoulos and Charles W Mims (1979)

• Fungi and slime molds were placed under the kingdom of their own, called Myceteae under the super kingdom Eukaryota.

• The kingdom was divided into three divisions and further the divisions were divided into sub –division, class and so on.

The kingdom Myceteae was sub divided into three major divisions:

• GYMNOMYCOTA - phagotrophic organisms with somatic structures devoid of cell walls.

• MASTIGOMYCOTA – primarily aquatic and had motile, flagellated spores or gametes; fungi with centrioles (also associated with the

formation and functioning of flagella); flagellate cells typically produced during the life cycle; nutrition typically absorptive; varying

from unicellular that becomes into a sporangium, to an extensive, filamentous, coenocytic mycelium; asexual reproduction typically by

zoospores; sexual reproduction by various means.

• AMASTIGOMYCOTA - fungi without centriole, no motile cells, nutrition absorptive, single-celled to mycelial with a limited or

extensive, septate or aseptate mycelium; asexual reproduction by budding, fragmentation, sporangiospores or conidia; sexual

reproduction is known, by various means; haplobiontic-haploid life cycle with zygotic meiosis.
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 Alexopoulos & Mims system of classification
Division I: Gymnomycota
• Slime molds; organisms having a noncellular and multinucleate creeping vegetative phase and a propagative spore-producing stage:
comprises Myxomycetes and Acrasiomycetes.
• The distinguishable characteristics of these organisms are, they ingest particulate nutrients and also lack cell walls during the vegetative
stage.
• This division is further divided into two subdivisions such as Acrasiogymnomycotina and Plasmodiogymnomycotina.
• Lack of a True Cell Wall: In some life stages, particularly during their amoeboid phase, Gymnomycota species do not have a cell wall,
allowing for greater mobility.
• Amoeboid Stage: These fungi are known for their unique life cycle, which includes an amoeboid, free-moving phase in which they
resemble protozoans rather than typical fungi.
• Reproduction: Gymnomycota generally reproduce through spore formation. Spores are often resistant and can survive adverse conditions
until they germinate when the environment is favorable.
• Plasmodium Formation: the amoeboid cells can aggregate to form a multinucleate, single-cell structure called a plasmodium, which can be
extensive in size and visible to the naked eye.
• Life Cycle Phases: They often display complex life cycles that alternate between a unicellular amoeboid phase and a multicellular
reproductive phase.
• Habitat: They are commonly found in moist and decaying organic matter, such as forest floors, where they play a role in decomposition.
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 Alexopoulos & Mims system of classification
Division I: Gymnomycota
Subdivision 1: Acrasiogymnomycotina
• The Acrasiogymnomycotina subdivision contains a single class known as Acrasiomycetes.
Class 1 - Acrasiomycetes
• Cellular slime molds
• Acrasiomycetes lack flagellated cells except for one species, Pocheina rosea.
• In the vegetative stage, free-living amoebae (like structure) aggregate to form a stalked sporocarp bearing
spores in a mucilaginous matrix.
• Some representative organisms of this class are Dictyostelium discoideum and Polysphondelium violaceum.
• This class contains two sub-classes such as Acrasiomycetidae and Dictyosteliomycetidae.

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Dictyostelium discoideum

Polysphondelium violaceum

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 Alexopoulos & Mims system of classification

Subdivision 2: Plasmodiogymnomycotina
It contains two classes such as
Class 1 - Protosteliomycetes
Class 2 - Myxomycetes.
• The true slime molds are included within the class Myxomycetes.
• Some important distinguishing characteristics of this class are; asexual reproduction by binary fission and
sporangiospores formation, and the sexual phase is absent.
• Physarum polycephalum is the representative organism of this class.
• This class contains following 3 subclasses:
• Subclass I: Ceratiomyxomycomycetidae: This subclass contains one order known as Ceratiomyxales.
• Sub Class II: Mycogasteomycetidae: This subclass contains four orders such as
a. Liceales, b. Echinosteleales, c. Trichlales and d. Physarales
• Sub Class III: Stemonitomycetidae: This subclass contains one order known as Stemonitales.

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Physarum polycephalum

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 Alexopoulos & Mims system of classification

Division II Mastigomycota
• Fungi in which spores and gametes are motile.
• This division contains flagellated lower fungi with absorptive nutrition, unicellular or filamentous, mycelium coenocytic.
• Flagellated Cells: A defining feature of Mastigomycota is the presence of flagella in their motile cells (spores or gametes). This allows
for movement in aquatic environments, which aids in reproduction and dispersal.
• Water Dependence: These fungi typically require water for dispersal of their flagellated spores and fertilization, as the motile spores
swim toward gametes or other structures.
• Saprophytic and Parasitic: Mastigomycota species can be saprophytic, feeding on decaying organic matter, or parasitic, infecting plants,
animals, or other fungi.
• Asexual and Sexual Reproduction: These fungi reproduce both asexually through motile spores (zoospores) and sexually through
gametes, which are also motile in some species.
• Cell Wall Composition: Their cell walls may contain cellulose rather than chitin, which distinguishes them from many true fungi.
• Morphology: Some species have hyphal or filamentous forms, but they also can exhibit simpler structures, such as unicellular or
multinucleate forms, depending on the lifecycle stage.
• Mastigomycota division consists of two subdivisions such as Haplomastigomycotina and Diplomastigomycotima.

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 Alexopoulos & Mims system of classification

Division II Mastigomycota
Subdivision I: Haplomastigomycotina
• This subdivision contains fungi with uni-or, bi-flagellate zoospores.
• Haplomastigomycotina contain three classes such as;
• Class 1 Chytridiomycetes: Containing fungi can produce
zoospores which are furnished with a single whiplash flagellum at
the posterior end.
• Class 2 Hyphochytridiomycetes: Includes motile cell containing
single tinsel flagellum at the anterior end.
• Class 3 Plasmodiophoromycetes: These are the parasitic fungi that
can produce biflagellate motile cells containing both the type of
flagella.

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 Alexopoulos & Mims system of classification

Subdivision II: Diplomastigomycotina

• The distinguishable characteristics of this subdivision are
Sexual reproduction - ooagamous
Zoospores are biflagellate.
• It consists of one class:
• Class 1 Oomycetes
• The Oomycetes class contains four order such as
a. Lagenidiales,
b. Saprolegnailes,
c. Leptomitales,
d. Peronosporales.

Zoospores: http://archive.bio.ed.ac.uk/jdeacon/microbes/zoospore.htm
Phytophthora 21
 Alexopoulos & Mims system of classification
Division III Amastigomycota
• The major distinguishable characters of these fungi are absorptive mode of
nutrition, spores lacking flagella, aseptate or septate mycelium.
• This division contains 4 subdivisions such as; Zygomycotina, Ascomycotina,
Basidiomycotina, and Deuteromycotina.
Subdivision I Zygomycotina
• This subdivision contains two classes such as Zygomycetes
and Trichomycetes.
Class I Zygomycetes: consist of six orders.
E.g. Rhizopus, Mucor etc
Class II Trichomycetes: consist of five orders.
Smittium sp.
E.g. Smittium sp

Rhizopus
Mucor

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 Alexopoulos & Mims system of classification
Subdivision II Ascomycotina
• Fungi with septate mycelium producing haploid ascospores in a sac-
like structures known as asci.
• This subdivision contains only one class - Ascomycetes
Class 1 Ascomycetes: This class contain five subclasses;
• Subclass I Hemiascomycetidae Contain three orders.
• Subclass II Plectomycetidae Contain Five orders
• Subclass III Hymenoascomycetidae Contain Ten orders
• Subclass IV Laboulbeniomycetidae Contain Two orders
• Subclass V Lowloascomycetidae Contain five orders

Saccharomyces (yeast) Aspergillus

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Penicillium chrysogenum
 Alexopoulos & Mims system of classification

Subdivision III Basidiomycotina

• The major distinguishable characters of these fungi are
septate mycelium, which can produce basidiospores
exogenously on various types of basidia.
• This subdivision contains only one class.
Class 1 Basidiomycetes:
• Consist of three subclasses such as:
• Subclass I Holobasidiomycetidae
• Subclass II Phragmobasidiomycetidae
• Subclass III Teliomycetidae

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Polyporus

Puccinia

Lycoperdon (puff ball)

Agaricus sp. 25
 Alexopoulos & Mims system of classification

Sub division IV Deuteromycotina (fungi imperfecti)

• It includes imperfect fungi in which sexual stage is unknown.
• It comprises a single form class.
Form Class Deuteromycetes - three form sub classes
Form sub class Blastomycetidae,
Form sub class Coelomycetidae Colletotrichum
Form sub class Hyphomycetidae

Fusarium sp. 26
Trichoderma sp.
Only for reference – not
in the syllabus