Fungi, like plants and animals, represent a unique kingdom in the taxonomic organization of organisms. They differ from other kingdoms in their method of obtaining nutrients, in that they employ absorbtive modes of nutrition. The fungal body is composed of long cellular tubes called hyphae. Such hyphae are found in the soil beneath the mushroom shown here and even compose the flesh of the mushroom itself. Hyphae aggregate into a larger structure called a mycelium. The mycelium, under certain environmental conditions, will give rise to an organ-like structure called a fruiting body. Mushrooms, like the one pictured on this page, are typical fruiting bodies. So beneath this mushroom, spreading throughout the soil, lies a mat-like mycelium that can give rise to several other mushrooms in the same area.

Fungi reproduce by spores, often contained in some sort of fruiting body. Spores are dispersed in some manner to other geographic areas. Reproduction in fungi may be sexual or asexual. Different fungi are classified by the method of sexual reproduction that they employ.

Some common fungi that produce spores suited for airborne dispersal and are thought to have allergenic qualities are Ascomycetes, Basidiomycetes, and Asexual Fungi. Myxomycetes spores are also dispersed in the air and may also be allergenic.