This division has many features in common with the Ascomycota: mycelia with chitinous cell walls that are regularly septate, presence of an extended dikaryon stage, yeast stage and presence of macroscopic fruiting bodies, in some taxa, and conidia are produced if an asexual stage is present. As in the Ascomycota and Zygomycota, the characteristic that defines this subdivision is the sexual spore stage. The sexual spores produced are basidiospores that are typically borne, exogenously, on horn-like sterigmata (sing.=sterigma) of basidia (sing.= basidium) (Fig. 1). The morphology of the basidium, however, is variable and a few of the variations are shown in the micrographs below (Figs. 2-4), and the variations observed below were once thought to be of considerable significance in the phylogeny of the Basidiomycota.

Holobasidium-t.jpg (10385 bytes) Figure 1: Unicellular basidium, with four sterigmata and basidiospores. Basidium illustrated to the left is commonly used as representative of the typical basidium.
Tremella_basidium-t.jpg (26381 bytes) Figure 2: Cruciate-septate basidium. This basidium is divided into four chambers. The basidium is named for the "cross" that can be seen when viewed,from above, through the microscope.
Transversely_septate_basidium-t.jpg (28130 bytes) Figure 3: Transversely septate basidium. This basidium resembles hyphal cells, with sterigmata . Because of its lack of differentiation, this was once considered to be a primitive basidium.
Tunning_Fork_basidium-t.jpg (31597 bytes) Figure 4: Tunning fork basidium. The basidium is named for its obvioius resemblance to a tunning fork. This basidium produces only two basidiospores.
Puccinia_Basidia-t.jpg (27270 bytes) Figure 5: Transversely septate basidiospores germinating from a rust teliospore. Basidiocarp is absent.

Three classes are currently recognized:

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