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basidium

(pl. basidia)

Terms discussed: -sterigmate, basidiomycete (pl. basidiomycetes), bisterigmate, heterobasidium (pl. heterobasidia), holobasidium (pl. holobasidia), homobasidium (pl. homobasidia), phragmobasidium (pl. phragmobasidia), sterigma (pl. sterigmata), tremelloid


See Also:
hymenium




Image of Pisolithus tinctorius from Jean Louis Émile Boudier (1904 - 1909) Icones mycologicae ou iconographie des champignons de France, principalement Discomycètes
Pisolithus tinctorius
Basidia are specialized end-cells on which the fungi that possess them produce their spores. The picture here shows various stages of spore-production on the basidia of Pisolithus tinctorius. In this case, you can see the spores becoming brown as they mature.

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Fungi that bear their spores on basidia are known as basidiomycetes, and are placed in the phylum Basidiomycota.

The spores are usually attached to the basidium by short spikes called sterigmata (singular: sterigma). There are usually four sterigmata (and four spores) to a basidium.


Image of Hydnangium carneum from Jean Louis Émile Boudier (1904 - 1909) Icones mycologicae ou iconographie des champignons de France, principalement Discomycètes
Hydnangium carneum
Basidia which bear only two spores are called bisterigmate. Basidia with some other number of spores are generally just identified with the number plus "-sterigmate". For another picture of bisterigmate basidia, see the entry for subhymenium.

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Image of Cantharellus cibarius from Joseph Henri Léveillé (1837) Sur le hymenium des champignons in Annales des Sciences Naturelles. Botanique
Cantharellus cibarius
For instance, chanterelles are usually (as in this picture) 5- to 7-sterigmate. Just be thankful we use the numbers, and there aren't a lot of extra prefixes to learn!


Image of Fomes fomentarius from Jean Louis Émile Boudier (1904 - 1909) Icones mycologicae ou iconographie des champignons de France, principalement Discomycètes
Fomes fomentarius
The basidia shown so far are all are of a type called holobasidia: they are made of a single cell and are more or less clavate, with sterigmata that are fairly small in proportion to the basidium. Gilled mushrooms, boletes, polypores, chanterelles, tooth fungi and crust fungi (Hymenochaetaceae) have this type of basidium, and are called Holobasidiomycetes. This type of basidium is also called a homobasidium.

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Other basidiomycetes have different types of basidia, which are called phragmobasidia or heterobasidia. These type of basidia are typical of the jelly fungi and the rusts and smuts.


Image of Pseudohydnum gelatinosum from Jean Louis Émile Boudier (1904 - 1909) Icones mycologicae ou iconographie des champignons de France, principalement Discomycètes
Pseudohydnum gelatinosum
Here, the development of one type of phragmobasidium can be seen: it starts off, in the top left, as just an end cell with a swelling at the end, but splits into two, and then four cells, each with its own sterigma. This type of basidium is known as a tremelloid basidium, and is typical of the genus Tremella. Fungi with this type of genus are placed in the order Tremellales.

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Image of Tremella from Jean Louis Émile Boudier (1904 - 1909) Icones mycologicae ou iconographie des champignons de France, principalement Discomycètes
Tremella
Many of the fungi with this sort of basidia are jelly fungi. As first discovered by Pierre-Augustin Dangeard, many jelly fungi form their basidia deep within the layer of jelly that covers their fruiting body. The sterigmata have to be extra-long in order to poke through the jelly that covers the basidium and lift the spores out into the open.

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Not all phragmobasidia are septate. Bisterigmate "tuning fork basidia", with two long sterigmata coming from a single cell, are typical of the genus Dacrymyces. Fungi with this type of basidia are placed in the order Dacrymycetales.

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Image of Dacrymyces from Jean Louis Émile Boudier (1904 - 1909) Icones mycologicae ou iconographie des champignons de France, principalement Discomycètes
Dacrymyces
This series of drawings shows the development of this type of basidium.

A third type of phragmobasidium is simply a string of four cells, each bearing its own sterigma and spore. Unfortunately, I don't have a picture of this type of basidium yet. This type of basidium is typical of the order Auriculariales and the classes Ustilaginales (the smuts) and Uredinales (the rusts).

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