CLASSIFICATION OF FUNGI
Kingdom—Fungi can be divided into various classes on the
basis of morphology of mycelium, mode of spore formation
and fruiting bodies.
1. Phycomycetes
The members of Phycomycetes are found in aquatic
habitats and on decaying wood in moist and damp places or
as obligate parasites on plants.
General characteristics of this class are as follows
(i) Mycelium is aseptate and coenocytic.
(ii) Hyphal wall contains microfibrils of cellulose, chitin
or both.
(iii) Asexual reproduction involves the endogenous
formation of sporangia. The sporangia function as
conidia in dry habitats and as mosporangia under
wet conditions.
(iv) Zoospores may be uniflagellate or biflagellate with I
flagella being anterior,
lateral or posterior.
A zoospore is formed by the fusion of two gametes.
(v) The gametes are similar in morphology (isogamous)
or dissimilar (anisogamous or oogamous).
(vi) Disease caused by the members of Phycomycetes are
white rust (Albugo), late blight of potato
(Phytophthora infestans), downy mildew (Peronospora
parasitica), etc.
Examples include Albugo (parasitic fungi on mustard)’
Rhizopus (the bread mould), Pythium, Plasmospard’
Phytophthora.
2. Ascomycetes
The members of Ascomycetes are commonly called as sac
fungi. They are mostly multicellular (Penicillium) and
rarely unicellular (yeast).
The common features of Ascomycetes are described below
(i) They are mostly terrestrial, some are aquatic. A
number of Ascomycetes are parasites on plants,
animals and humans.
(ii) Mycelium is branched and septate. It may consist of
distinct hyphae or the same may aggregate to
produce prosenchyma and pseudoparenchyma.
(iii) They are saprophytic, decomposers parasitic or
coprophilous (growing on dung).
(iv) The asexual spores are conidia produced exogenously
on the special mycelium called conidiophores
Conidia on germination produce mycelium.
(v) Sexual spores are called ascospores (sing. ascus)
endogenously which are produced in sac-like asci.
These asci are arranged in different types of fruiting
bodies called ascocarps. Each ascus bears
4-8 ascospores, sometimes numerous.
(vi) Sexual reproduction occurs by gametangia] contact
resulting in formation of oospores.
Examples include Penicillium, Aspergillus, Claviceps,
Neurospora, Yeast, etc. Neurospora is used extensively in
biochemical and genetic work.

3. Basidiomycetes
These are terrestrial, saprotrophic and parasitic forms, also
known as club fungi. Many of them attack trees. A few
species form mycorrhizal association.
(i) The mycelium is branched and septate.
(ii) Asexual spores are generally not found, but vegetative
reproduction by fragmentation is common.
(iii) Sex organs are absent but plasmogamy occurs by the
fusion of two vegetative or somatic cells of different
strains or genotypes. The resultant structure is a
dikaryon which ultimately gives rise to basidium.
(iv) Karyogamy and meiosis take place in basidium
producing four basidiospores. The basidiospores are
exogenously produced on the basidium (Pl. basidia).
The basidia are arranged in fruiting bodies called
basidiocarps.
Examples include Agaricus compestris (edible mushroom),
Puccinia (cause rust), Ustilago (cause smut diseases),
Amanita (toad stools), bracket fungi, Lycoperdon (puftballs),
Armillaria (honey mushroom).
4. Deuteromycetes
These are commonly known as imperfect fungi because
only the asexual or vegetative phases of these fungi are
known. These are mostly terrestrial, only few of them are
aquatic, e.g., Tricladium, Pyricularia.
The characteristics of Deuteromycetes are
(i) The mycelium is septate and branched. Cells are
usually multinucleate and septa possess simple
pores. The lamp connections are absent.
(ii) Asexual reproduction by the formation of
conidia or sometimes by oidia and chlamydospores.
(iii) Sexual reproduction is not certain.
(iv) Mycelium structure and conidia indicate that most
of the Deuteromycetes belong to Ascomycetes whose
sexual reproduction is not known.
Knowledge Plus
Annals are much less susceptible to parasitic fungi than are
plants. Only about 50 species of fungus are known to parasitise
human and other animals, but these few species cause
considerable damage. The general term for such a fungal
infection is mycosis.