The most common association that the Agaricales order of fungi develop with other organisms is a mutualistic symbiosis with the roots of vascular plants.  The fungus forms what is called ectomycorrhizae which is a fungal coating around the outside of plant roots.  This provides the plant with a larger surface area for which to absorb water and nutrients.  In return, the fungus receives sugars that the plant produces via photosynthesis.  Although rare compared to the ectomycorhizzae, Agaricales may associate with green algae or cyanobacteria in a symbiosis termed a lichen.  Here, the fungus takes up the bacteria and provides a stable environment while receiving nutrients from the photosynthesizing bacteria.  See the British Soldier Lichen site for more lichen info and the Nostoc site as an example cyanobacteria.  Other members of the Agaricales order can parasitize plants or other fungi such as certain species of Armillaria, Athelia, Moniliopthora and Mycena.  A few may even capture or parasitize certain vertebrates and invertabrates!

The parasitism of other fungi (mycoparasitism) is prevalent in certain basidiomycota, especially the Tremellomycetee (Bandoni 1984).  Other symbiotic Basidiomycota form associations with insects, including leaf-cutter ants, termites, scale insects, woodwasps and bark beetles (Wheeler and Blackwell, 1984; Mueller et al., 1998).

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