Wednesday, February 3, 2010

What are the main differences among the major groups of fungi?

Fungi are classified into units called Divisions. There are 4 divisions based primarily on variations of sexual reproduction. The names of the divisions are based on the sexual structure that characterizes that group of fungi.

1. Division Zygomycota: These are mostly terrestrial fungi that live in soil or on decaying plant or animal material. Their hyphae are coenocytic, with many haploid nuclei. Asexual spores, usually wind swept, are produced by structures called sporangia, at the tips of aerial hyphae. Sexual reproduction involves the formation of resistant bodies called zygosporangia that can remain dormant when the environment is too harsh for growth. Examples are black bread mold ( Rhizopus stolonifer).

Division Ascomycota: These are sac fungi. They range from unicellular yeast to large cup fungi. The sexual reproductive structure is the asci, a small sac like structure. These asci are packed into large fruiting structures called ascocarps. The hyphae are multicellular septate structures. They lack sporangia but reproduce asexually by producing chains of spores at the tip of specialized hyphae. These spores are called conidia. Two types of spores are produced by this type of fungus, conidia and ascospores. Conidia are asexual, while the ascospores are sexual. These fungi are important in decomposing lignin and collagen of dead plants and animals. Some are mutualistic ( lichen) and many are parasitic to plants ( powdery mildew and Dutch elm disease).

Division Basidomycota: The mushroom, shelf fungi, puffballs and stink horns are examples of this division. The name is derived from the sexual reproductive structure called the basidium. The club like shape gives the name to some of the most common fungal types in this division.What are the main differences among the major groups of fungi?
The major divisions (phyla) of fungi are mainly classified based on their sexual reproductive structures. Currently, five divisions are recognized:

* The Chytridiomycota are commonly known as chytrids. These fungi produce zoospores that are capable of moving on their own through liquid menstrua by simple flagella.

* The Zygomycota are known as zygomycetes and reproduce sexually with meiospores called zygospores and asexually with sporangiospores. Black bread mold (Rhizopus stolonifer) is a common species that belongs to this group; another is Pilobolus, which shoots specialized structures through the air for several meters. Medically relevant genera include Mucor, Rhizomucor, and Rhizopus. Molecular phylogenetic investigation has shown the zygomycota to be a polyphyletic group.

* Members of the Glomeromycota are also known as the arbuscular mycorrhizal fungi. Only one species has been observed forming zygospores; all other species only reproduce asexually. This is an ancient association, with evidence dating to 400 million years ago.

* The Ascomycota, commonly known as sac fungi or ascomycetes, form meiotic spores called ascospores, which are enclosed in a special sac-like structure called an ascus. This division includes morels, some mushrooms and truffles, as well as single-celled yeasts and many species that have only been observed undergoing asexual reproduction. Because the products of meiosis are retained within the sac-like ascus, several ascomyctes have been used for elucidating principles of genetics and heredity (e.g. Neurospora crassa).

* Members of the Basidiomycota, commonly known as the club fungi or basidiomycetes, produce meiospores called basidiospores on club-like stalks called basidia. Most common mushrooms belong to this group, as well as rust (fungus) and smut fungi, which are major pathogens of grains.

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