FUNGI – DEFINITION, CHARACTERISTICS, CLASSIFICATION​

The term ‘Fungi’ is used for those plants which lack chlorophyll and are, therefore, heterotrophic. Being the members of Thallophyta, their plant body is simple and is not differentiated into root, stem and leaves.

The branch that deals with fungi is known as ‘Mycology’. It included the study of mushrooms only to begin with. The credit for laying the foundation of present day mycology goes to Italian Botanist Pier’ Antonio Micheli who included his researches on fungi in a book-Nova Plantarum Genera published in 1729.

Fungi include 100,000 species, of which 40,000 are known to be valid species leaving 60,000 to be investigated and described in future. The earlier fungal taxonomists included bacteria also in this group, the practice which is now completely discarded. The members of this heterotrophic group exist either as parasities or saprophytes. Special absorbing organs called haustoria are developed for this purpose. Thallus is either coenocytic (aseptate) or septate forming compact structures like mushrooms, morels, etc. Hyphal system (filamentous) forms a thallus and is called mycelium. The cell wall is typically made of chitin while the reserve food occurs mainly in the form of glycogen. Both asexual and sexual methods of reproduction are known in fungi. Asexual reproduction is through different types of spores like zoospores, conidiospores, basidiospores, chlamydospores, etc. Sexual reproduction in fungi is extremely reduced. In lower members distinct sexual reproduction is present but is gradually reduced in higher members and finally it is found to be absent in Fungi imperfecti.

The diseases caused by this group have rendered it sufficient economic importance. The members of this group attack plants as well as animals including the human beings. Since the fungi are principal agents of decay, so through the decomposition of organic matter, they play an essential role in the nutrition of the green plants. Contrary to these harmful activities, fungi serve as food, used in preparation of medicines and antibiotics, and are employed in many industrial processes.

Fungi have been variously classified by numerous mycologists, time and again: Basically the group was divided into five classes-Myxomycetes, Phycomycetes, Ascomycetes, Basidiomycetes and Deuteromycetes. This classification was the most convenient. However, the trend now is to treat fungi as a kingdom rather than as a sub-group of Thallophyta equal in rank to algae. One of such classifications was proposed by G.C. Ainsworth (1973).

CLASSIFICATION OF FUNGI

CHARACTERS OF FUNGI

KINGDOM MYCOTA (FUNGI)

• Chlorophyll absent
• Reserve food glycogen
• Cell wall of fungal cellulose

DIVISION I. MYXOMYCOTA

• Thallus without cell walls
• Thallus a naked mass of protoplasm

CLASS :- PLASMODIOPHOROMYCETES

• Plasmodium parasitic within the cells of host plants

Order :- Plasmodiophorales

• Swarm cells anteriorly biflagellate

Family :- Plasmodiophoraceae

• Vegetative development within the host cells
  Example :- Plasmodiophora

DIVISION II. EUMYCOTA

• Presence of definite cell wall throughout the vegetative phase.

SUB-DIVISION 1. MASTIGOMYCOTINA

•  Presence of motile spores or zoospores
• Oospores produced as a result of sexual reproduction

CLASS 1. CHYTRIDIOMYCETES

•  Thallus usually unicellular
• Zoospores uniflagellate (flagella whiplash type)

Order :- Chytridiales

• Asexual reproduction by posteriorly uniflagellate zoospores

Family :- Synchytriaceae

• Thallus endobiotic, holocarpic, directly forms a sorus or prosorus
  Example :- Synchytrium

CLASS 2. OOMYCETES

• Thalli usually mycelial (mycelium aseptate)
• Zoospores biflagellate (posterior flagellum whiplash type and anterior tinsel type)
• Cell wall cellulosic

Order 1. Saprolegniales

• Mycelial thallus extensive and without a conspicuous hold fast
• Members aquatic, often called water molds
• Sporangia cylindrical

Family :- Saprolegniaceae

• Oogonium with many eggs and lacks perioplasm
  Examples :- Saprolegnia, Achlya

Order 2. Peronosporales

• Sexual reproduction aplanogametic and oogamous
• Primarily terrestrial-in soil or parasitic on vascular plants
• oogonium with a single egg surrounded by periplasm

Family 1. Pythiaceae

• Sporangiophores similar to somatic hyphae or if different, indeterminate in growth
  Examples :- Pythium, Phytophthora

Family 2. Peronosporaceae

• Sporangiophores dichotomously branched, determinate
• Sporangia borne singly at the tips of branches
  Examples :- Sclerospora, Peronospora

Family 3. Albuginanceae

• Mycelium intercellular and provided with knob-like haustoria
• Conidia in basipetal chains on clavate, unbranched conidiophores
  Example :- Albugo

SUB-DIVISION 2. ZYGOMYCOTINA

• Asexual reproduction by non-motile spores, aplanospores, perfect stage sporezygospore formed

CLASS :- ZYGOMYCETES

• Gametangia morphologically similar
• Sexual reproduction results in the formation of zygospores

Order :- Mucorales

• Mostly saprophytic
• Asexual reproduction by typical non-motile aplanospores

Family 1. Mucoraceae

• Sporangia with many spores and well developed columella
• Sporangial wall relatively thin and easily breakable or deliquescent
• Suspensors rarely tong-like
  Examples :- Rhizopus, Mucor

Family 2. Pilobolaceae

• Sporangia with many spores with moderate sized columella
• Sporangium wall thickened above and not breaking up or deliquescent.
• Sporangium violently discharged or passively discharged as a unit
• Suspensor always tong-like
  Example :- Pilobolus

SUB-DIVISION 3. ASCOMYCOTINA

• Mycelium septate, if not reproduces by budding
• Ascospores borne endogenously in ascus
•  Ascospores in definite numbers, in multiples of two, usually eight.

CLASS 1. HEMIASCOMYCETES

• Thallus yeast-like or unicellular
• Asci naked and formed directly from the zygotes
• Ascogenous hyphae and ascocarps not formed

Order :- Endomycetales

• Mostly saprophytes
• Zygote unicellular, forms ascus directly

Family :- Saccharomycetaceae

• Cells multiply by budding
  Example :- Saccharomyces

Class 2. Plectomycetes

• Ascocarp, a cleistothecium

Order 1. Erysiphales

• Ectoparasites

Family :- Erysiphaceae

• Aerial mycelium hyaline
• Enormous production of conidia on host surface gives it a white powdery appeamce
  Examples. Erysiphe, Sphaerotheca, Phyllactinia

Order 2. Eurotiales

• Ascocarp – a cleistothecium

Family :- Eurotiaceae

• Asci scattered, 8-spored, thin walled, ascospores unicellular
• Hymenium not formed
• Peridium (outer wall of cleistothecium) of closely interwoven hyphae
  Examples :- Aspergillus, Penicillium

Class 3. Pyrenomycetes

• Ascocarp, a perithecium

Order :- Sphaeriales

• Ascocarp borne singly or in stroma, dark, membranous or carbonous

Family 1. Sordariaceae

• Perithecia dark coloured, not in stroma, free
• Ostiole lined by periphyses
  Example :- Neurospora

Family 2. Xylariaceae

• Perithecia embedded in stroma
• Stroma consisting entirely of fungus tissue
• Ascospores dark and inequilateral
  Example :- Xylaria

Family 3. Clavicipitaceae

• Perithecia develop on fleshy stroma, ostiolate
• Perforated cap at the apex of ascus
• Ascospores long, narrow, often breaking up into short segments
  Example :- Claviceps

Class 4. Discomycetes

• Ascocarp, an apothecium

Order :- Pezizales

• Apothecia fleshy or leathery
• Apothecia usually not in stroma
• Asci opening by a lid or operculum

Family 1. Pezizaceae

• Apothecia not differentiated into stipe andpileus
  Examples. Pyronema, Peziza, Ascobolus

Family 2. Helvellaceae

• Apothecia not cup-shaped
• Apothecia differentiated into stipe and pileus
  Example :- Morchella

SUB-DIVISION 4. BASIDIOMYCOTINA

• Mycelium septate
• Characteristic reproductive body is basidium
• Basidiospores usually four, produced exogenously

CLASS 1. TELIOMYCETES

• Basidiocarp lacking
• Teliospores or chlamydospores in sori or scattered
• parasitic on vascular plants

Order 1 :- Ustilaginales

• Mycelial hyphae in the host inter-as well as intracellular
• Telio- or teleutospores mostly intercalary, basidiospores not on sterigmata
• Basidiospores indefmite in numbe

Family Ustilaginaceae

• Chlamydospores formed in the host tissue from hyphal cells
  Examples :- Ustilago, Sphacelotheca

Order 2. Uredinales

• Teleutospores formed terminally
• Four basidiol’pores per basidium, Basidiospores on sterigmata
• Infected plant rusty in colour

Family :- Pucciniaceae

• Teleutospores stalked
• Teleutospores free or united but never in the form of layer
  Examples :- Puccinia, Uromyces

CLASS 2. HYMENOMYCETES

• Basidiocarp usually well-developed
• Mostly saprobic.

Sub-class :- Holobasidiomycetidae

• Basidia aseptate (holobasidia), club-shaped.

Order 1. Exobasidiales

• Basidiocarp present
• Basidia covering the surface of host tissue

Family :- Exobasidiaceae

• Basidiocarp septate prior to germination
• Basidia club-shaped and formed externally
  Example :- Exobasidium

Order 2. Agaricales

• Basidia borne on lamellae
• Basidiocarp soft and putrescent

Family :- Agaricaceae

•  Basidiocarp fleshy
• Gills narrow in section
  Example :- Agaricus

Order 3. Aphyllopborales

• Basidiocarp developed gymnocarpously on the outer side
• Texture of basidiocarp not soft and putrescent

Family :- Polyporaceae

•  Basidia line the inner surface of the pore or tube
• Pores or tubes generally deep
  Examples :- Polyporus

CLASS 3. GASTEROMYCETES

• Basidiocarps pennanently closed (angiocarpous)
• Basidia do not become exposed until the spores are mature

Order :- Lycoperdales

• Glebal cavities usually not separating from the peridium or from each other
• Gleba powdery
• Spores light coloured and small

Family :- Lycoperdaceae

• Peridium distinguished into two layers
• Presence of capillitium among spores
  Example :- Lycoperdon

SUB-DIVISION 5. DEUTEROMYCOTINA

• Mycelium septate
• Perfect stages not known
• Reproduction by asexual means only

CLASS 1. HYPHOMYCETES

• Mycelium sterile or bearing spores directly or on special branches
• Not aggregated in pycnidia or acervuli

Order :- Moniliales

• Conidia borne on free conidiophores

Family 1. Dematiaceae

• The mycelium, conidiophores and usually the conidia are brown or black in colour
  Examples :- Alternaria, Cercospora, Helminthosporium

Family 2. Moniliaceae

• Conidia are borne on free conidiophores, pycnidia or acervuli never fonned
  Example :- Piricularia

Family 3. Tuberculariaceae

• Conidiophores usually rather short arising more or less radially from sporodochia
  Example :- Fusarium

CLASS 2. COELOMYCETES

• Thallospores or conidia bome in pycnidium or acervulus

Order :- Melanconiales

• Conidia in acervuli, immersed in substratum
• Conidia black or light coloured, accompanied by setae or not

Family :- Melanconiaceae

• Single fonn-family
• Example :- Colletotrichum