Prior to the introduction of the five kingdoms, fungi were classified with plants. However, they are different from plants in the composition of their cell walls. While the plant cell wall is made up of cellulose, the wall of fungi is made of chitin.
Characteristics of Kingdom Fungi:
1. They can be either unicellular e.g. Yeast or multicellular e.g. Mushroom, Rhizopus.
2. Their cell walls are composed of chitin.
3. They are important decomposers in the ecosystem.
4. They reproduce asexually by budding (e.g. yeast), spore formation (e.g. bread mould) or by fragmentation.
5. They reproduce sexually by conjugation e.g Rhizopus.
6. Some fungi form mutualistic associations with algae, such as in Lichens. (Lichens can live on bare rocks and can survive harsh environmental conditions.)
7. Fungi carry out extracellular digestion i.e. outside the body and absorb the nutrients.
8. They are non-green plants lacking chlorophyll.
9. They have no true roots, stems or leaves.
10. Fungi are saprobes i.e. they obtain their food from dead decaying organic matter, as such they recycle nutrients in the biosphere. They can be found on rotting logs, dead leaves, fruits, bread and leather.
11. Some fungi cause diseases such as athlete’s foot, examples include Mushrooms, Rhizopus, Yeast, Toadstools, Puffballs, and Brackets.
12. Their body is composed of a network of thread-like structures called hyphae. The branching hyphae form a network called mycelium (plural: mycelia)
13. Examples of fungi are bread mould, rhizopus, slime mould, mushroom, mucor, mildew, yeast and toadstools.
14. They store carbohydrates in form of glycogen.
Hyphae (Functions, Types):
Hyphae perform a variety of functions in fungi.
- They contain the cytoplasm or cell sap, including the nuclei containing genetic material.
- They absorb nutrients from the environment.
- They transport these nutrients to other parts of the fungus body.
There are two types of hyphae;
ii. Aseptate/Non-septate or Coenocytic hyphae.
The difference is the presence or absence of cross walls called septa. Septate hyphae have septa while aseptate hyphae lack septa.
Classification Based on Spore Formation:
Kingdom Fungi are classified into the following based on the formation of spores:
1. Class Zygomycetes (formerly Phycomycetes):
- They are like algae or algae-like fungi.
- They form their spores within the sporangium.
- They are non-septate i.e. they have no cross walls in the hyphae.
- They reproduce sexually and asexually.
- In asexual reproduction, sporangia develop at the tips of the reproductive hyphae. The sporangia contain a large number of spores which are easily dispersed by wind.
- The spores germinate when they land on suitable surfaces.
- They reproduce sexually when conditions are not favourable such as extreme temperatures and shortage of food supply.
- Examples are Mucor and Rhizopus.
2. Class Ascomycetes (Sac Fungi):
- They are septate i.e. they have cross walls in their hyphae.
- They have mycelium which branches into numerous hyphae.
- They possess fruiting bodies called ascocarp which bear sac-like structures called asci (singular: ascus) which contain sexual spores. When mature, the spores are released and germinate into individual hyphae.
- Spores are born on conidium (asexual) or asci (sexual).
- Unicellular yeast reproduces asexually by fission or budding.
- Examples are Penicillium, Saccharomyces, and Yeast.
3. Class Basidiomycetes (Club Fungi):
Members of the Basidiomycota are commonly known as the club fungi or basidiomycetes.
- They are septate.
- They have mycelium.
- They have fruiting bodies called basidium e.g. Mushrooms.
4. Class Deuteromycetes:
- They are pathogenic or parasitic.
- They have an imperfect life cycle with no sexual stages.
- Asexual reproduction occurs by conidia.
- They are septate e.g. Fusarium causes ringworm and athlete’s foot. Some cause rust in plants.
- Deuteromycetes are characterized by the presence of septate mycelium.
- Some of the examples are Cercospora, Colletotrichum, Trichoderma, and Pyricularia.