Alexopoulos (1962) designated the
term Mycota for all fungi. Mycota is
given the rank of division. The division Mycotais divided into two
sub-divisions – Myxomycotina (true
slime moulds) and Eumycotina (true
fungi).
The
sub-division Eumycotina, i.e., true fungi are divided into two main groups –
the Lower Fungi and the Higher Fungi.
A. THE
LOWER FUNGI (PHYCOMYCETES):- This
group of fungi has comparatively a simple thallus which in some is unicellular
and in others filamentous (mycelium). They reproduce asexually by sporangiospores (generally motile,
rarely non-motile), rarely by conidia.
Lower fungi are divided into 6 classes on the basis of presence or absence of
motile cells in the life cycle and the number, form and position of flagella on
motile cells.
With Motile Cells
1. Class Chytridiomycetes: It includes the lower fungi in
which the motile cells have a single flagellum of whiplash type inserted at
the posterior end. The members of this class are called Chytrids.
2. Class
Hyphochytridiomycetes: The motile cells (zoospores) possess a single
flagellum of tinsel type which is inserted at the interior end.
3. Class Plasmodiophoromycetes: The
motile cells (zoospores) are biflagellate. Both the flagella are of whiplash
type, but one of these is longer than the other. The longer one has a
sharply pointed end and the shorter one has a blunt end.
4. Class Oomycetes: The motile cells are
biflagellate. The two flagella are usually of nearly equal length. One of
these, points forward while the other trails behind. The former is tinsel
type and the later is whiplash type.
With Non-motile Cells
5. Class Zygomycetes: Motile cells are absent. Asexual
reproduction takes place by sporangiospores
which are uncapsulated and wind disseminated.
6. Class Trichomycetes: The motile
cells are lacking. The asexual cells are produced exogenously at the tips of
special hyphae (conidiophores) and are called the conidia.
B. THE HIGHER
FUNGI:- The
somatic phase consists mostly of a mycelium which is usually septate. No motile
cells are produced in the life cycle. The higher fungi comprise the following 3
classes –
7. Class Ascomycetes: The
characteristic spores of the sexual or perfect stage are endogenous in origin
and are called ascospores. They are
produced within a specialized sac like structures called the asci. Plasmogamy takes place by the
fusion of the gametangia or somatic hyphae. Somatic phase is usually septate
mycelium, which multiplies asexually by conidia. Rarely it is unicellular
(Yeast) and is propagated by budding
or rarely by fission.
8. Class Basidiomycetes: The
characteristic spores of the sexual or perfect stage are exogenously in origin
and are called the basidiospores.
They are borne externally usually on club shaped structures called basidia. The somatic phase consists of
a simple or complex mycelium with or without clamp connections. Sexual organs
are lacking. Plasmogamy, however takes place by hyphal fusion.
9. Class Deuteromycetes or Fungi
Imperfecti: The fungi included in this class are the higher fungi in which
sexual or perfect stage is unknown. The somatic phase consists of a septate
mycelium which multiplies asexually by conidia.
The conidia are produced on conidiophores which may occur isolated or may be
aggregated to form complex structures such as synnema, pycnidia and acervuli.
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