Basidiomycetes are fungi most commonly seen in forests and open fields. They include the mushrooms, toadstools, puffballs, bracket fungi (involved in decay of wood) and the rusts and smuts (economically important parasites of cereal crops). This is another large group of over 25,00 species. The plant body is generally filamentous with central pores in the cross-walls between cells. Vegetative filaments are usually dikaryotic, i.e., functionally diploid but with two unfused haploid nuclei paired in cells. The definitive feature of the group is the production of a club-shaped structure called a basidium where nuclear fusion and meiosis occurs. Haploid basidiospores produced in this structure migrate out into four small bleps. The rusts and smuts have septate basidia, whereas basidia in mushrooms and puffballs are non-septate (Fig.1).

Basidia are generally produced upon germination of resting dikaryotic spores in rusts and smuts. Basidia in other basidiomycetes are housed in a fruiting body called a basidiocarp. The fruiting body consists of compacted dikaryotic filaments. There are many types characteristic for each species. In some mushrooms, thousands of basidia line gills within a stalked cap (Fig. 2, Fig. 3). Basidia line pores or teeth in others, are surfaced exposed in the jelly fungi and stinkhorns, or reside in enclosed basidiocarps in puffballs. Basidiocarps of a few species are cultivated for food. Many wild types are edible, but anyone interested in eating wild mushrooms should be aware that a fungus edible to one person without ill effects may be poisonous to another. Accurate identification is also important, as many edible species are either closely related or are morphologically similar to poisonous ones.

Although a sexual process occurs in a majority of basiodimycetes, differentiated sex organs do not develop in members of this group. Establishment of long-lived dikaryotic filaments can be accomplished by fusion of different strains of haploid filments derived from basidiospores. No gametes and no flagellated cells can be found in any members of this group.