To a naturalist viewing fungi in the field there would hardly be any reason to suspect the various Basidiomycota to be related to one another. Some produce large fleshy fruiting bodies, others cause disfiguring diseases of plants without any obvious fruiting bodies and some are barely visible at all. However, careful study of their life histories and close examination with a microscope shows that all produce basidia at some time in their lives. The basidia themselves vary considerably but always produce external spores, and these are mostly four in number or, more rarely, in multiples of four.
Three subphyla of Basidiomycota are generally recognized: the Pucciniomycotina, the Ustilaginomycotina and the Agaricomycotina. In the older literature this would have been presented as the rust fungi, the smut fungi and the fleshy fungi, or even as two groups, the Heterobasidiomycetes and the Homobasidiomycetes. Although these older groupings certainly relate in many repects to the newer ones, the use of modern genetic techniques have revealed a rather more complicated picture. Using these techniques it is possible to assign almost any fungus to one of the three modern subphyla; but it is more difficult to do this on the basis of features we can observe.
Although it is possible, at least roughly, to define the three subphyla of Basidiomycota this requires the introduction of some new concepts and terms.
Cruciate basidium (Figure 1)
Holobasidium (Figure 2)
Phragmobasidium (Figure 3)
Tuning fork basidium (Figure 4)
Condition in the Dikary where cells contain two compatible nuclei and the the binuceate condition is maintained during cell division. See the discussion of reproduction in the Dikarya for further information.
Condition in the Dikary where cells contain a single nucleus. See the discussion of reproduction in the Dikarya for further information.
Sterigmata (sing. sterigma)
Horn-like extensions from the basidium on which basidiospores are produced.
At a very early stage in its development at basidium may become thick-walled and go into a form of dormancy. This thick-walled cell, usually containing a diploid nucleus, may resemble a spore and may even become detached and disseminated to a new location. Later, usually at the beginning of a new growing season, the nucleus undergoes meiosis and the basidium completes its development. Some teliospores are multicellular and produce a basidium from each cell.
Pucciniomycotina - the rust fungi and their allies
Ustilaginomycotina - the smut fungi and their allies
Agaricomycotina - the mushrooms and their allies