Basidiomycetes form sexual spores externally from a structure called a basidium. Four basidiospores develop on appendages from each basidium. These spores serve as the main air dispersal units for the fungi. The spores are released during periods of high humidity and generally have a night-time or pre-dawn peak concentration in the atmosphere.

General Structure and Shape:

Basidiospores are generally characterized by an attachment peg (called a hilar appendage) on its surface. This is where the spore was attached to the basidium. The hilar appendage is quite prominent in some basidiospore, but less evident in others. An apical germ pore may also be present. Many basidiospores have an asymmetric shape due to their development on the basidium. Basidiospores are typically single-celled (without septa), and typically range from spherical to oval to to oblong, to ellipsoid or cylindrical. The surface of the spore can be fairly smooth, or it can be ornamented.