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The Wonderful World of Fungi
What is a Fungus?
Along with bacteria, these are the most important decomposers in the
mycelium - the entire body of the fungus
hyphae - (singular, hypha) threadlike structures of which the mycelium is composed
thallus - another term for the mycelium; "body"
spore - haploid propagule produced via meiosis
sporangium - structure within which spores are produced (either
sexually or asexually, depending on life cycle stage)
The Fungal Life Cycle
a fungus is haploid for most of its life cycle
individuals are one of two complementary mating types generally called "+" and "-"
diploidy is brief, followed by meiosis that gives rise to spores
all fungi have essentially the same life cycle, though the parts look different:
all are absorptive heterotrophs
they secrete digestive enzymes onto their nutrient source and absorb the product
The main structural support in the cell walls is chitin
Except for one small group (chytrids), fungi lack cellulose
no true tissues; the thallus is composed of coenocytic--and sometimes septate--hyphae
- saprobic fungus - absorptive heterotroph that feeds on dead, organic
matter. Such a fungus is said to be a "saprobe."
- parasitic fungus - absorptive heterotroph that feeds on living tissue
- In parasitc fungi specialized hyphae, haustoria, create a nutrient pathway between fungus and host cell
the main storage carbohydrate is glycogen (as in animals)
Fungi exist in different forms
- mold - rapidly growing, asexually reproducing hyphal form
- yeast - unicellular, usually in liquid or moist environments
Major Fungal Taxa
The earliest fungal phylogenies were based on mode of sexual reproduction. Molecular data have resulted in significant revisions.
These fungi retain primitive characters that may provide clues about fungal origins.
- Most are aquatic, suggesting an aquatic origin of the Fungi.
- Some are free-living saprobes, others are parasites of protists, plants and aquatic
- Like all fungi, they have chitin in the cell walls
- one aberrant group of chytrids has cellulose in the cell walls (unique among fungi)
- chytrids are the only fungi to retain flagellated gametes (zoospores)
- no flagella are found in any other fungi--just in chytrids (primitive!)
Ascomycota - The Sac Fungi
About 75% of all described fungal species are ascomycetes.
- named for the microscopic pouch where zygotes undergo meiosis to become (asco)spores: ascus ("sac" in Latin)
Basidiomycota - The Club Fungi
These are the most commonly recognized fungi, and the most commonly eaten by us (for good or bad reasons).
- named for the microscopic structure where zygotes undergo meiosis to become (basidio)spores: basidium("club" in Latin)
Glomeromycota - Vital to Ecosystems
Mycorrhizae - "fungus roots"
This is a symbiotic relationship between a fungus and a plant root. (What does each partner get out of the relationship?)
- Vesicular Arbuscular Mycorrhizae (V.A.M.) - association between a glomeromycete and a plant
- Ectomycorrhizae - association between asco- or basidiomycete and a conifer
or flowering plant (usually large trees).
Some of the most valuable edible organisms in the world are truffles, various species of
Be sure to review the different types of symbiosis.
Arthrobotrys (a Deuteromycete) nabs nematodes and other small prey
We eat many species--but be sure you know what you're doing!
rainforest ascomycete parasitoids that infect arthropods
various dermatophytes and other nasties
respiratory pathogen Histoplasma capsulatum
Dutch Elm disease threatens native U.S. populations of elm trees
some fungi which infect rotting food (such as grain crops) can be
carcinogenic (e.g., some species of Aspergillis or highly toxic
(ascomycete ergots - a smut disease which infects plants).
Fungal toxins are collectively
known as mycotoxins, and are economically important.
A chytrid fungus, Batrachochytrium dendrobatidis, has been implicated in the recent large-scale extinctions of amphbians, worldwide.
- Ergots are
sclerotia (resting stage of the fungus) that replace the ovaries of
- ergots are loaded with highly toxic alkaloids that can
damage central nervous system, cause smooth muscle contraction, necrosis,
hallucinations and temporary insanity
Lichens - a symbiotic association between a fungus
and a photoautotroph.
- ubiquitous, but most notably in harsh climates (dry, cold)
- fungus provides habitat for the
autotroph; algae provide photosynthates for the fungus
- absorb nutrients directly from the atmosphere,
so are very sensitive to air pollution
- Vital primary producers in harsh environments, such as tundra.
- Lichens are the original source of the compound used to make litmus
paper (an old-fashioned way to tell if a solution is acidic or
Biologists put the FUN in FUNgi.