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Coelomycetes Classification Essay

In this article we will discuss about the classification of fungi by various botanists.

Classification of Fungi by Bauhin (1623):

Bauhin (1623) is the first who described about 100 species of fungi in his book ‘Pinax Theatri Botanici’.

But the detailed classification of fungi was first proposed by Elias Fries in his book “Systema Mycologicum”, published in three volumes between 1821 and 1831, where he divided fungi in four classes:

(i) Coniomycetes,

(ii) Hyphomycetes,

(iii) Gastromycetes, and

(iv) Hymenomycetes.

Classification of Fungi by Saccardo:

Later, Saccardo (1884) in his book “Sylloge Fungorum” divided fungi into six classes:

(i) Schizomycetes,

(ii) Myxomycetes,

(iii) Phycomycetes,

(iv) Ascomycetes,

(v) Basidio- mycetes and

(vi) Deuteromycetes.

Later, much more handy system of classification was pro­posed by Gwynne-Vaughan and Barnes (1926). In their classification, Myxomycetes were not considered as fungi and were included by them as forms resembling fungi.

The outlines of the classification proposed by them are:

Key to Classes of Fungi:

A. Mycelium usually aseptate … Phycomycetes Mycelium septate.

B. Sexual reproduction results in formation of asci containing ascospores … Ascomycetes.

C. Sexual reproduction results in formation of basidium bearing basidiospores…………………………………… Basidiomycetes.

D. Sexual reproduction not known (ascospores and Hsidiospores absent)…Deuteromycetes or Fungi imperfecti.

Key to Subclasses:

A. Phycomycetes

i. Mycelium absent or rudimentary. ………………………………………………..Archimycetes

(e.g., Synchytrium, Olpidium) Mycelium well-developed.

ii. Oospore produced after sexual union of dissimilar gametes ………………………………………………..Oomycetes

(e.g., Pythium, Phytophthora)

iii. Zygospore produced after sexual union of gametangia ………………………………………… Zygomycetes

(e.g., Rhizopus, Mucor)

Key to Subclasses:

B. Ascomycetes

i. Round ascocarp contains asci, arranged irregularly ……………………. Plectomycetes

(e.g., Penicillium, Erysiphae)

ii. Cup-shaped ascocarp contains asci, arranged in parallel series …………………………………………………. Discomycetes (e.g., Ascobolus, Peziza)

iii. Flask-shaped ascocarp contains asci, arranged in parallel series …………………………………………………… Pyrenomycetes

(e.g., Daldenia, Xylaria)

Key to Subclasses:

C. Basidiomycetes

1. Number of basidiospores per basidium are indefinite………. Hemibasidiomycetes

(e.g., Tilletia, Ustilago)

Number of basidiospores per basidium are definite.

ii. Basidium septate …Protobasidiomycetes

(e.g., Puccinia, Gymnosporangium)

iii. Basidium aseptate…Autobasidiomycetes

(e.g., Agaricus, Polyporus)

Classification of Fungi by I. E. A. Gaumann and B. O. Dodge (1928):

E. A. Gaumann and B. O. Dodge (1928) also did not consider the Myxomycetes as fungi. They classified fungi based on both the phases (i.e., haploid and diploid) of life cycle; structure of thallus and organs of fructifications.

They divi­ded the fungi into four classes are:

1. Archimycetes:

Thallus naked; diploid stage in the life cycle is represented only by the zygote.

2. Phycomycetes:

Thallus with distinct cell wall; diploid stage in the life cycle is repre­sented only by the zygote.

3. Ascomycetes:

Thallus highly developed with distinct cell wall. Dikaryotic mycelium is formed by plasmogamy during sexual repro­duction and meiosis takes place in special reproductive organ, the ascus. Ascospores are developed endogenously in the ascus, which remain naked or enclosed in fruit body.

4. Basidiomycetes:

Thallus as in Ascomycetes; Dikaryotic mycelium is formed by plasmo­gamy; the fruit body is known as basi- diocarp. The basidiospores develop exo- genously on the basidium on/inside the basidiocarp.

Classification of Fungi by E. A. Bessey (1950):

E. A. Bessey (1950) proposed a more elabo­rate system of classification of fungi, based on reproductive characteristics.

The outline of the classification is:

A. Lower fungi:

Fruit bodies are not formed.

1. Class:

Phycomycetes:

Plants one-celled or with coenocytic mycelium. Sexual reproduction results the development of oospore or zygospore.

B. Higher fungi (Phylum. Carpomyceteae):

Fruit bodies are formed.

1. Class.

Ascomyceteae:

Fruit body con­tains asci, where ascospores are formed endogenously.

2. Class:

Basidiomyceteae:

Fruit body contains basidia, where basidiospores are formed exogenously.

3. Class:

Fungi imperfecti:

Sexual stage not known.

Classification of Fungi by G. W. Martin (1961):

G. W. Martin (1961) included slime moulds under fungi. His classification is based on septation of hypha and characteristics of spore.

The outline of the system is:

A. Myxomycetes:

Plant body having naked protoplast.

B. Eumycetes:

Plant body may be unicellular or filamentous and are true walled fungi.

It is divided into four classes:

1. Class:

Phycomycetes:

Mycelium coenocytic.

2. Class:

Ascomycetes:

Mycelium septate and sexual spore i.e., ascospores deve­lop endogenously.

3. Class:

Basidiomycetes:

Mycelium sep­tate and sexual spore i.e., basidiospores develop exogenously.

4. Class:

Deuteromycetes:

Mycelium sep­tate and sexual reproduction absent. Reproduction takes place only by ase­xual spores.

Classification of Fungi by C. J. Alexopoulos (1962):

C. J. Alexopoulos (1962) also included slime molds under fungi and placed them as Division Mycota and it was divided into two subdivisions: Myxomycotina (wall-less form) and Eumycotina (true, walled fungi).

The outline of his classifica­tion is:

Division:

Mycota:

Microscopic, unicellular or filamentous thallus with chitinous or cellulosic cell wall containing typical eukaryotic nucleus. Reproduction takes place both asexu­ally and sexually.

A. Subdivision. Myxomycotina:

Plant body is Plasmodium.

1. Class. Myxomycetes:

Vegetative phase is plasmodium. Reproduction takes place by very small multinucleate spore.

B. Subdivision. Eumycotina:

Vegetative phase is either unicellular or branched mycelium with distinct cell wall. Hyphae are coeno­cytic (aseptate and multinucleate) or septate. Each cell may be uni-, bi- or multinucleate. Reproduction by asexual (spore) or sexual (gamete) means.

The sub-divisions has been .divided into eight natural classes and one form-class.

These are:

Class. Chytridiomycetes:

Motile cells with single whiplash flagellum placed posteriorly.

Class. Hypochytridiomycetes:

Motile cells with single tinsel flagellum placed anteriorly.

Class. Oomycetes:

Vegetative phase con­sists of multinucleate and well-developed mycelium. Motile cells have two flagella i.e., biflagellate consists of one whiplash and the other tinsel type.

Class. Plasmodiophoromycetes:

Multi­nucleate thallus without cell wall, remains parasitically inside the host cells. Motile cells are with two whiplash flagella of unequal in length.

Class. Zygomycetes:

Well-developed coenocytic (multinucleate and aseptate) mycelium grows either parasitically or saprophytically. Motile cells are absent.

Class. Trichomycetes:

Multinucleate simple or branched thallus; mostly parasite on arthopods.

Class. Ascomycetes:

Well-developed mycelium with septate hyphae. Ascospores are produced endogenously inside ascus.

Class. Basidiomycetes:

Well-developed mycelium with septate hyphae. Basidiospores are produced exogenously on basidium.

1. Form-class. Deuteromycetes:

Well-developed mycelium with septate hyphae. Sexual phase unknown. Reproduces mainly by asexual means.

Classification of Fungi by V. C. J. Alexopoulos and C. W. Mims (1979):

Later, C. J. Alexopoulos and C. W. Mims (1979) placed fungi and slime molds under the kingdom of their own, called Myceteae under the superkingdom Eukaryonta. The kingdom is divided into three divisions and further the divi­sions are divided into sub-division, class and form-class.

The outline of the classification is given:

Kingdom. Myceteae (Fungi):

Achlorophyllous, saprobic or parasitic organisms with uni­cellular or more typically, filamentous soma (thallus), usually surrounded by cell walls that characteristically consists of chitin and other complex carbohydrates, nutrition absorptive, except in the slime molds (Division Gymno- mycota) where it is phagotrophic, propagation typically by means of spores produced by various types of sporophores; asexual and sexual reproduction usually present.

The kingdom is subdivided into three major divisions:

A. Division. Gymnomycota:

Phagotrophic organisms with somatic structures devoid of cell walls:

a. Subdivision. Acrasiogynomycotina:

1. Class. Acrasiomycetes

b. Subdivision. Plasmodiogymnomycotina:

1. Class. Protosteliomycetes

2. Class. Myxomycetes

B. Division. Mastigomycota:

Fungi with centrioles; flagellate cells typically produced dur­ing the life cycle; nutrition typically absorp­tive; varying from unicellular that becomes converted into a sporangium, to an exten­sive, filamentous, coenocytic mycelium, asexual reproduction typically by zoospores; sexual reproduction by various means:

a. Subdivision. Haplomastigomycotina

1. Class. Chytridiomycetes

2. Class. Hyphochytridiomycetes

3. Class. Plasmodiophoromycetes

b. Subdivision. Diplomastigomycotina

1. Class. Oomycetes

C. Division. 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, where known, by various means; haplobiontic-haploid life cycle with zygotic meiosis.

a. Subdivision. Zygomycotina

1. Class. Zygomycetes

2. Class. Trichomycetes

b. Subdivision. Ascomycotina

1. Class. Ascomycetes

c. Subdivision. Basidiomycotina

1. Class. Basidiomycetes

d. Subdivision. Deuteromycotina

1. Form class. Deuteromycetes.

Classification of Fungi by Ainsworth G. C. (1966, 71, 73):

Ainsworth G. C. (1966, 71, 73) proposed a more natural system of classification of fungi. This classification is based on morphology, espe­cially of reproductive structure. He includes fungi along with slime molds under the kingdom Mycota.

Based on the presence or absence of Plas­modium and pseudoplasmodium; the kingdom Mycota is further divided into two divisions:

Myxomycota i.e., slime molds and Eumycota or true fungi. Divisions are subsequently divided into subdivision, class, subclass, order, family and then to genus. According to his classification, division ends in mycota, subdivision in mycotina, class in mycetes, subclass in mycetidae order in ales and family in aceae.

A schematic outline of Ainsworth’s (1973) classification is given:

Kingdom: Mycota

Important features:

i. Free-living, parasitic or mutualistic symbionts, devoid of chlorophyll.

ii. Cell wall composition is very variable, majority contain chitin and glucan.

iii. Reserve food materials are oil, mannitol and glycogen.

iv. Except some unicellular members, majority are filamentous.

A. Division. Myxomycota:

Wall-less organisms possess either a Plasmo­dium (a mass of naked multinucleate protoplasm having amoeboid movement) or a pseudoplasmo­dium (an aggregation of separate amoeboid cells). Both are of slimy consistency, hence slime molds.

1. Class. Acrasiomycetes (cellular slime molds)

2. Class. Hydromyxomycetes (net slime molds)

3. Class. Myxomycetes (true slime molds)

4. Class. Plasmodiophoromycetes (endo- parasitic slime molds).

B. Division Eumycota (True fungi, all with walls):

a. Subdivision Mastigomycotina (motile cells – zoospores present, perfect state spore-oospore).

1. Class. Chitridiomycetes (unicellular, zoospore with single whiplash flagellum).

2. Class. Hyphochytridiomycetes (uni­cellular, zoospore with single tinsel flagellum).

3. Class. Oomycetes (aseptate myceli­um, zoospores with two flagella).

b. Subdivision. Zygomycotina (mycelium aseptate, perfect state spore-zygospore).

1. Class. Zygomycetes (mycelium immersed in the host tissue).

2. Class. Trichomycetes (mycelium not immersed in the host tissue).

c. Subdivision. Ascomycotina (yeasts or septate mycelium, perfect state spore- ascospores formed in ascus, usually within ascocarp).

1. Class. Hemiascomycetes (no asco­carp, asci naked).

2. Class. Loculoascomycetes (fruit body an ascostroma, asci bitunicate i.e., 2-walled).

3. Class. Plectomycetes (fruit body cleistothecium, asci unitunicate i.e., 1-walled).

4. Class. Laboulbeniomycetes (fruit body perithecium, asci unitunicate, exoparasite of arthopods).

5. Class. Pyrenomycetes (fruit body perithecium, asci unitunicate, not parasitic on arthopods.

6. Class. Discomycetes (fruit body apothecium, asci unitunicate).

d. Subdivision. Basidiomycotina (yeast or septate mycelium, perfect state spore – basidiospore formed on a basidium).

1. Class. Teliomycetes. Basidiocarp lacking, teliospores grouped in sori or scattered within the host tissue, parasitic on vascular plant.

2. Class. Hymenomycetes. Basidio- carp present. Hymenium is com­pletely or partly exposed at matu­rity. Basidiospore ballistospores.

3. Class. Casteromycetes. Basidiocarp present. Hymenium enclosed in basidiocarp. Basidiospore not ballistospores.

(e) Subdivision. Deuteromycotina or Fungi imperfecti. Yeast or septate mycelium. Perfect state unknown.

1. Class. Blastomycetes. Budding (Yeast or Yeast like) cells with or without pseudomycelium. True mycelium lacking or not well-developed.

2. Class. Hyphomycetes. Mycelia ste­rile or bearing asexual spore directly or on conidiophore, in various aggregation.

3. Class. Coelomycetes. Mycelial; asexual spore formed in pycnidium or acervulus.

Schematic representation of the outline with figure, the classification of G.C. Ainsworth (1973) is given:

Schematic outline of the classification of G. C. Ainsworth (1973):

The classification of Ainsworth (1973) has been followed in this book. Later, Webster (1980), Deacon (1980) and Hudson (1986) also proposed their classifications. Among all the above classifications, Ainsworth’s classification has been accepted by many mycologists, with some comments.

Say for example, the Mastigo- mycotina is a composite grouping covering all fungi that form motile flagellated zoospores. Among others, unrelated classes like Chitridio- mycetes and Oomycetes were included in the same group. Oomycetes has indeed quite a different evolutionary origin to that of most other fungi.

Classification of Fungi by Hawksworth et al. (1983 and 1995):

Ten years after the classification of Ainsworth (1973), Hawksworth et al. (1983) revised Ainsworth’s classification in the 7th edi­tion of the “Dictionary of the Fungi”.

The changes made by them are:

1. The Division Myxomycota divided into eight classes instead of four classes.

2. The Sub-division Ascomycotina is directly divided into thirty seven (37) orders and arranged alphabetically; there is no classes in-between.

3. The subdivision Basidiomycotina is divided into four classes instead of three, where class Teliomycetes is replaced by Uredinio- mycetes and Ustilaginomycetes.

4. In the sub-division Deuteromycotina, the class Blastomycetes was not considered.

Later, Hawksworth et al. (1995) thoroughly revised the classification in the 8th edition of the “Dictionary of the Fungi”. The classification was based on the sequence of 18s rRNA among the different members.

Though members of fungi show similarity in their morphology, mode of nutrition and ecology, but the higher dissimilarity is observed in the base sequences of their 18s rRNA (or more precisely in the DNA coding for it), which is now considered as the most important parameter to determine the genetic relationship. Thus, it shows that the fungi are polyphyletic aggregation of unrelated members.

Based on the above fact and phylogenetic consideration, the entire fungal community are now segregated out and placed them under three different Kingdoms Fungi, Straminopila (Chromista) and Protozoa.

Based on comparison of several factors such as, 18s rRNA, cytoskele- ton protein, chemical features like chitin, mito­chondrial codon UGA coding for tryptophan instead of termination, storage of glycogen, elon­gation factors and morphological structure of motile cells like male gamete in animal and zoospores in fungi, there is close similarity of fungi with animals than to other two groups like Straminopila and Protozoa.

The different taxa considered in this system are:

Further the species are divided into varieties, biological strains, physiological races, etc.

The different taxa considered in this system along with their ‘ending’ are:

Phylum — mycota

Sub-phylum — mycotina

Class — mycetes

Sub-class — mycetidae

Order — ales

Family — aceae

But the genera and species have no standard ending. In this system, division has been replaced by phylum and all taxa are written in italics.

All the three groups are placed under the Domain Eukaryota. Out of three kingdoms, king­dom Fungi includes only fungi, but the other two kingdoms include non-fungal phyla also.

The earlier consideration of the sub-division Deutero­mycotina representing the asexual stages of Ascomycotina and Basidiomycotina (Ainsworth 1973, Hawksworth et al1983) was now reconsidered as a formal taxon as they are not a monophyletic group. The members are described under Mitosporic fungi.

Phylum Ascomycota:

Important characteristics:

1. Vegetative body is unicellular or com­monly well developed, branched septate mycelium with uni- or multinucle­ate cells having perforated septa.

2. Mostly, the cell wall is composed of chitin and glucans, but in unicellular form, it is composed of glucans and mannans.

3. Vegetative reproduction takes place by fragmentation (in filamentous form), fission and budding (in unicellular form).

4. Asexual reproduction takes place by non-motile spores, such as conidia, oidia and chlamydospores.

5. Sexual reproduction takes place by gametangial copulation (Saccharomy­ces), gametangial contact (Penicillium), somatogamy (Morchella) or spermatiza- tion (Polystigma).

6. Complete absence of motile structures.

7. The product of sexual reproduction is the ascospores grown inside a small specialised sac-like structure, called ascus.

8. The fruit bodies (inside which ascus developed) are the ascocarps. The asco- carps may be cleistothecium (Penicilli­umi), apothecium (Ascobolus), peritheci­um (Daldenia) or ascostroma (Elsinoe veneta).

Common genera:

Saccharomyces, Penicilli­um, Daldenia, Ascobolus, Morchella etc.

Phylum Basidiomycota:

Important characteristics:

1. Presence of well-developed, branched and septate mycelium having simple (e.g., Ustlaginales and Uredinales) or dolipore (e.g., Auriculariaceae, aphyllo- phorales and Agaricales) septum (Fig. 4.2B & 4.2D).

2. The mycelial cells contain one nucleus, called monokaryotic i.e., primary mycelium or two nuclei, called dikaryo­tic i.e., secondary mycelium. The secon­dary mycelia may organise and form fruit body, called tertiary mycelium.

3. The cell wall is mainly composed of chitin and glucans.

4. Reproduction

(a) Vegetative reproduction takes place by budding and fragmentation.

(b) Asexual reproduction takes place by conidia, oidia or chlamy­dospores. This is lacking in some higher taxa of this subdivision.

(c) Sex organs are absent. During sexu­al reproduction, the dikaryotic cell is formed by somatogamy, sperma- tisation or by buller phenomenon. The dikaryotic phase persists for long period of time. Karyogamy occurs in basidium mother cell and forms diploid nucleus, which is ephemeral (short lived). 4-haploid basidiospores are formed by meio- sis. Basidiospores are developed exogenously on the horn-shaped structure, the sterigmata (generally 4) on the basidium.

5. Basidia are of two types: Holobasidium (aseptate) e.g., Agaricus, Polyporus etc. (Fig. 4.56A) and Phragmobasidium (sep­tate) e.g., Puccinia, Ustilago (Fig.4.56B) etc.

6. Except in lower forms (Puccinia, Ustilago), secondary mycelia by aggre­gation form fruit body, the basidiocarp [Agaricus, Polyporus etc.). The number of spores’ on each basidium is common­ly 4, but 2 or more than 4 are also pre­sent.

Common genera:

Agaricus, Polyporus, Puccinia etc.

Class Basidiomycetes Class Teliomycetes Class Ustomycetes

Phylum. Chytridiomycota:

Important characteristics:

1. Vegetative body is coenocytic and thalloid, either globose or ovoid structure, either an elongated simple hypha, or well, developed mycelium.

2. Cell wall is mainly made up of chitin and glucan.

3. Nuclear division is intranuclear and centric type.

4. Members of this group produce motile cells at some stage of their life cycle.

5. Motile cells (zoospores and gametes) possess single posteriorly placed, whiplash type of flagellum except a few polyflagellate cells.

6. Sexual reproduction takes place by planogametes developed in gametan­gia. The fused gametes form zygote. Zygote on germination develops either into a resting spore or resting sporan­gium except’ a few those develop diploid thallus.

Common genera:

Synchytrium, Monoble- pharis, Rhizophidium etc.

Class Chitridiomycetes.

Phylum Zygomycota:

Important characteristics:

1. The thallus is normally haploid, consist­ing of coenocytic mycelium and its wall contains chitin and chitosan.

2. The mycelium contains cell organelles like other fungi, except typical golgi bodies and centriole.

3. Asexual reproduction takes place by aplanospores.

4. Sexual reproduction takes place by gametangial copulation results in the formation of zygospore.

Common genera:

Mucor, Rhizopus, Phyco- myces, Cunninghamella etc.

Class Trichomycetes

Class Zygomycetes

Kingdom Straminopila or Chromista (i.e., pseudo- fungi).

Phylum Hyphochytriomycota:

It is a very small group, comprising of about 23 known species.

Important characteristics:

1. The organisms are thalloid, soil-inhabiting or aquatic, chitrid-like.

2. Cell wall contains both chitin and cellu­lose.

3. Thalli are either holocarpic or eucarpic. The holocarpic thalli are endobiotic and converted into a zoosporangium. In eucarpic forms, the thalli may consist of a single reproductive organ bearing a branched rhizoidal system or may be polycentric with septate and branched hyphae.

4. Motile cells (zoospores) possess single anteriorly placed flagellum, converted with flagellar hairs, which developed inside zoosporangium and are released through discharge tubes.

5. Sexual reproduction has not been demonstrated conclusively in any mem­ber. But some evidence suggestive of sexual cycle has been described for Anisolpidium ectocarpi parasitises on Ectocarpus mitchelIae. Suspected zygote has been reported in some, but meiosis has not been reported.

Common genera:

Rhizidiomyces, Reessia, Hyphochytrium etc.

Phylum Labyrinthulomycota:

(Net Slime Molds)

Important characteristics:

1. Members are found primarily in estuarine (a wide tidal mouth of a river) and near shore habitat; associated with algae, leaves of higher plants and orga­nic debris.

2. Members are mostly saprobic or weak parasites and exhibit nutrition through absorption.

3. Vegetative body is a net slime mold.

4. Presence of an ectoplasmic net-work of anastomosing, branched, wall-less filaments, produced by cells with a specialized cell surface organelle, the sagenogen or bothrosome.

5. Cell walls are composed of scales derived from Golgi.

6. Zoospores are flagellate, heterokont (unequal flagella) type. Flagella are laterally inserted. Larger one is tinsel, directed anteriorly and the shorter one is whiplash, directed posteriorly.

Common genera:

Labyrinthula, Thrausto- chytrium etc.

Phylum Oomycota:

Important characteristics:

1. Members of Oomycetes are found to grow in both fresh water and salt water as well as in terrestrial habitat.

2. They are either unicellular or filamen­tous, composed of profusely branched and coenocytic hyphae.

3. Septa develop in older region and also at the base of reproductive structures.

4. Cell wall is composed primarily of β- glucans, but also contains hydroxylpro- line, an amino acid; and small amount of cellulose.

5. Cells contain mitochondria with tubular cristae and with various types of bio­chemical and molecular characteristics.

6. Cell divisions (both mitotic and meiotic) are intranuclear and centric (i.e., the nuclear envelop remains intact until the end of division and centrioles are pre­sent at the poles of the dividing nuclei).

7. Unicellular forms are holocarpic, but filamentous forms are eucarpic.

8. Asexual reproduction takes place by means of biflagellate zoospores with shor­ter whiplash and longer tinsel flagella.

9. Zoospore ultrastructure shows various characteristics.

10. Sexual reproduction is oogamous and takes place by gametangial contact and which produces thick-walled sexual spore, the oospore.

11. Meiosis takes place in the developing gametangia (antheridia and oogonia).

Common genera:

Pythium, Peronospora, Albugo etc.

Kingdom Protozoa (i.e., the slime moulds).

Phylum Plasmodiophoromycota:

(Endoparasitic Slime Molds)

This group is commonly known as endo­parasitic slime molds. They are obligate parasites grow on algae, aquatic fungi and higher plants (commonly in the roots).

Important characteristics:

1. Members of this class are obligate para­sites (i.e., biotrophic) on fresh water algae, aquatic fungi and higher plants (commonly in the roots).

2. Vegetative body consists of a naked holocarpic plasmodium.

3. Plasmodia are of two types in their life cycle:

Sporangiogenous plasmodium (forms sporangium) and cytogenous- plasmodium (gives rise to cyst i.e., res­ting spore).

4. Zoospores biflagellate, having equal fla­gella of whiplash type situated in oppo­site direction, the shorter one in ante­rior and longer one in posterior side.

Common genera:

Plasmodiophora, Octo- myxa, Sorodiscus etc.

Phylum Dictyosteliomycota:

(Dictyostelid Cellular Slime Molds)

Important characteristics:

1. These are saprobic slime molds, grow in the middle of organic debris like dung, decaying plants and also in soil.

2. Somatic phase is microscopic and the fructifications are minute, inconspicu­ous (not easily noticed) and ephemeral (short-lived).

3. The somatic amoebae have filose pseudopodia and a nuclear envelope persisting up to later stage.

4. Somatic amoebae aggregate together to form a pseudoplasmodium.

5. The amoebae never fuse together, but retain their individuality with full co­operation as member of an association till the formation of sorocarp (Gr. sorus, heap; karpos, fruit).

6. The sorocarp is differentiated into two regions: stalk and spores. On germina­tion, spores develop into myxamoeba.

Common genera:

Dictyostelium, Polysphon- dylium etc.

Phylum Acrasiomycota

(Acrasid Cellular Slime Molds)

Members of this group are commonly known as Acrasid Cellular Slime Molds. They are found profusely in the upper layer of humus in deciduous forests and in cultivated lands.

Important characteristics:

1. Somatic phase mainly consists of amoe­boid cells or myxamoebae.

2. Myxamoebae aggregate to form a pseu­doplasmodium, which develops fruit body.

3. Lack of flagellated cells except in Pocheina rosea.

4. Fruit bodies may be sorocarp (in Dictyo­stelium) or sporocarp (in Protostelium).

Common genera:

Dictyostelium, Protos­telium etc.

Phylum Myxomycota:

They are commonly known as true slime molds or plasmodial slime molds, found in damp places especially on old wood and other decom­posing plant parts.

Important characteristics:

1. Somatic body is a free-living plasmo­dium.

2. They feed on yeast cells, protozoa, fun­gal spores and other substances.

3. Reproduction takes place by asexual and sexual means.

Asexual reproduction takes place by fragmentation in plasmodium or by binary fission in myxamoebae.

Sexual reproduction takes place by fusion between flagellated zoo­spores or myxamoeba to form zygote, from which multinucleate plasmodium develops by mitotic divisions. They develop different types of fructification. These are sporangium, aethalium and plas- modiocarp (Fig.4.11 D-G). Meiosis takes place during spore formation in the fructification.

Common genera:

Ceratiomyxa, Physarum etc.

Class Myxomycetes

Class Protosteliomycetes.

Home >> Diversity and classification >> True fungi >> Dikarya >> Asexual Dikarya >> Coelomycetes

COELOMYCETES

Coelomycetes are asexual Dikarya that produce their conidia inside some kind of enclosing structure. If this structure completely surrounds the conidia it is called a pycnidium; if the conidia are borne in a more open structure with a wall only around the lower part it is an acervulus. The large round structure in the picture at right is a pycnidium of the fungus Sphaerellopsis filum. This fungus is a parasite of rust fungi and occurs within their spore-bearing structures. In the picture you can see the urediniospores of the rust as numerous oval bodies surrounding the pycnidium of the Sphaerellopsis. The pycnidium here is very light coloured where it is sunken in the host tissues but dark on top. This is a common phenomenon among pycnidial fungi. Most pycnidia release their spores in a wet mass that is extruded out through the apical pore (ostiole). These often collect in large amounts and are either transported away by insects or will flow along with rain water.

Growing as a parasite on rust fungi is a rather unusual place to find a coelomycete. More commonly these fungi grow on living and dead plants. Some can become a nuisance to humans when they grow where they are not wanted. The specimen of Phoma herbarum pictured at left was orginally found embedded and growing in silicone sealant used to waterproof a meat-packing establishment near Toronto. All of the sealant had to be removed and replaced. Species of Phoma regularly turn up on materials in indoor environments and may be responsible for some of the dark brown to black mould growth seen on painted surfaces subject to moisture, such trim around showers and bathtubs and on window frames and sills.



The pycnidia considered so far have been simple flask-shaped structures with a single internal cavity. However, some pycnidia and acervuli can be highly complex and be composed of several cavities. The picture above is an example of one of these. This fungus, Libertella betulina commonly occurs on recently-killed birch logs. The first signs that it is there will be the small orange tendrils arising through small breaks in the bark, as figured in the left panel. A closer examination (centre panel) reveals that these tendrils have oozed out like toothpaste from its tube. In the right panel the structures have been cut in half with a razor blade to reveal what is below the bark. Here we can see that there are several chambers each producing orange conidia in massive numbers. These are then extruded out through one or more ostioles.


Bothrodiscus berenice, the species figured above, produces yet another sort of compound structure. Here the pycnidia are embedded together inside small goblet-shaped structures on the surface of balsam fir twigs. The picture at far left shows three of these "goblets" while the one to the right presents a cross section through the goblet to reveal the layer of pycnidia on its surface.


Home >> Diversity and classification >> True fungi >> Dikarya >> Asexual Dikarya >> Coelomycetes