3.6.1: Characteristics

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Fungi with the following structures can be placed in the Basidiomycota*:

*It is important to note that these features may look different or not be present at all in some groups of Basidiomycota, such as the rusts (Pucciniomycotina) and smuts (Ustilagomycotina). However, there are many physiological and genetic similarities that support grouping these organisms together in the Basidiomycota.

Basidia and Basidiospores

Both karyogamy and meiosis occur within a cell called the basidium. Haploid basidiospores from atop projections on the basidum called sterigmata (sing. sterigma). There are generally four spores, as shown in the image below, though the number of spores produced can vary by species. For example, the mushroom you are likely most familiar with, Agaricus bisporus (though you probably know it as a crimini or button mushroom at its immature stage and portobello at maturity), only produces two spores on each basidium (bi- meaning two).

A microscopic view of basidiospores being produced on basidia — Figure \(\PageIndex{1}\): A section through the gills of a mushroom. On the left, a basidium has four basidiospores sitting atop its four sterigmata. On the right, the spores have been released and the sterigmata are easier to distinguish. Photo by Maria Morrow, CC-BY-NC.

Clamp Connections

Basidiomycetes maintain their dikaryotic (n+n) state in each hyphal compartment by making structures called clamp connections. These are not always present, but provide a helpful identification feature when they are!

A clamp connection and septum labeled in an image of hyphae from a microscope — Figure \(\PageIndex{2}\): These two images show hyphae from a mushroom. In the image on the left, a clamp connection is visible at the septum. In the image on the right, four clamp connections are indicated by arrows. Photos by Maria Morrow, CC-BY-NC.

Hyphae with arrows indicating clamp connections where septa are located, appearing as bumps on the hyphae. — Figure \(\PageIndex{2}\): These two images show hyphae from a mushroom. In the image on the left, a clamp connection is visible at the septum. In the image on the right, four clamp connections are indicated by arrows. Photos by Maria Morrow, CC-BY-NC.

Complex Septations

Diagram of a dolipore septum — Figure \(\PageIndex{3}\): The complex dolipore septum found in basidiomycetes. This is not a feature that can be seen with the naked eye or in a standard microscope. "In hyphae of basidiomycete fungi, parenthesomes (1) "cap" a dolipore septum (2). The cell wall (3) swells around the septal pore to form a barrel-shaped ring. Perforations in the parenthesome allow cytoplasm to flow between (4) and (5)." Miguelferig, CC0, via Wikimedia Commons.