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Classifications of Fungi

Division Chytridiomycota

  • Chytridiomycota: earliest fungi; evolved from protists and retained flagella
  • Originally placed in Kingdom Protista
  • Share many characteristics with fungi:
    • Absorptive nutrition
    • Chitin cell walls
    • Hyphae
    • Enzymes / metabolism

Zygomycota – “zygote fungi”

  • Zygomycota: decomposers, pathogens, and some form mycorrhizal associations with plants
  • Sexual Reproduction – zygosporangia: resistant to heat/cold and site of karyogamy
  • Asexual reproduction: haploid spores  
  • Coenocytic
  • Grow rapidly

Zygomycetes

  • Zygosporangia, which are resistant to freezing and drying, can survive unfavorable conditions
    • Some zygomycetes, such as Pilobolus, can actually “aim” their sporangia toward conditions associated with good food sources

Ascomycota – “sac fungi”

  • Ascomycota: important plant parasites & saprobes
  • Sexual Reproduction – asci (sing. = ascus)
  • Asex. Reprod: enormous numbers of asexual spores called conidia
    • Conidia are not formed inside sporangia; they are produced asexually at the tips of specialized hyphae called conidiophores
  • Cup fungi, morels, truffles
  • Yeast - Saccharomyces
  • Decomposers, pathogens, and found in most lichens

Division Basidiomycota: club fungi

  • Basidiomycetes: important decomposers of wood / plant material
  • Named after transient diploid stage: basidium
  • Include:
    • Mycorrhiza-forming mutualists
    • Mushroom-forming fungi
    • Plant parasites e.g. rusts and smuts
  • Characterized by dikaryotic mycelium that reproduces sexually via basidiocarps

Life Cycle of a Mushroom-Forming Basidiomycete

  • Haploid basidiospores grow into short-lived haploid mycelia: under certain conditions, plasmogamy occurs
  • Resulting dikaryotic mycelium grows forming mycorrhiza or mushrooms (basidiocarps)
  • Mushroom cap supports and protects gills: karyogamy in the terminal, dikaryotic cells lining the gills produces diploid basidia
  • Resulting basidium immediately undergoes meiosis producing 4 haploid basidiospores
  • Asexual reproduction less common than in ascomycetes

Deuteromycetes

  • Rapidly growing fungus with no sexual stages
  • May develop into a sexual fungus, producing zygosporangia, ascocarps or basidiocarps
  • Molds with no known sexual stage are known as Deuteromycota or imperfect fungi:
    • Penicillium
    • Flavor for blue cheeses

Yeasts

  • Unicellular: reproduce
    • Asexually by budding
    • Sexually by producing asci or basidia
  • Saccharomyces cerevisiae is most important domesticated fungus:
    • Baking and brewing
    • Model organism
  • Can cause problems:
    • Rhodotorula: shower curtains
    • Candida: “thrush”

Mold

  • Rapid growth
  • Asexual spores
  • Human importance:
    • Food spoilage
    • Food products
    • Antibiotics, etc.