A basidium (pl., basidia) is a microscopic, spore-producing structure found on the hymenophore of fruiting bodies of basidiomycete fungi. The presence of basidia is one of the main characteristic features of the Basidiomycota. A basidium usually bears four sexual spores called basidiospores; occasionally the number may be two or even eight. In a typical basidium, each basidiospore is borne at the tip of a narrow prong or horn called a sterigma (pl. sterigmata), and is forcibly discharged upon maturity.

The word "basidium" literally means "little pedestal", from the way in which the basidium supports the spores. However, some biologists suggest that the structure more closely resembles a club. An immature basidium is known as a basidiole.

Basidium Structure

Most basidiomycetes have single celled basidia (holobasidia), but in some groups basidia can be multicellular (a phragmobasidia). For instance, rust fungi in the order "Uredinales" have four-celled phragmobasidia that are transversely septate; some jelly fungi in the order Tremellales have four-celled phragmobasidia that are cruciately septate. Sometimes the basidium (metabasidium) develops from a probasidium, which is a specialized cell which is not elongated like a typical hypha.

Mechanism of basidiospore discharge

In most basidiomycetes, the basidiospores are ballistospores--they are forcibly discharged. The propulsive force is derived from a sudden change in the center of gravity of the discharged spore. Important factors in forcible discharge include Buller's drop, a droplet of fluid that can be observed to accumulate at the proximal tip (hilar appendage) of each basidiospore; the offset attachment of the spore to the subtending sterigma, and the presence of hygroscopic regions on the basidiospore surface.

Upon maturity of a basidiospore, sugars present in the cell wall begin to serve as condensation loci for water vapor in the air. Two separate regions of condensation are critical. At the pointed tip of the spore (the hilum) closest to the supporting basidium, Buller's drop accumulates as a large, almost spherical water droplet. At the same time, condensation occurs in thin film on the adaxial face of the spore. When these two bodies of water coalesce, the release of surface tension and the sudden change in the center of mass leads to sudden discharge of the basidiospore. Remarkably, Money (1998) has estimated the initial acceleration of the spore to be about 10,000 g.

Successful basidiospore discharge can only occur when there is sufficient water vapor available to condense on the spore.

Evolutionary loss of forcible discharge

Some basidiomycetes lack forcible discharge, although they still form basidiospores. In each of these groups, spore dispersal occurs through other discharge mechanisms. For example, members of the order Phallales (stinkhorns) rely on insect vectors for dispersal; the dry spores of the Lycoperdales (puffballs) and Sclerodermataceae (earth balls and kin) are dispersed when the basidiocarps are disturbed; and species of the Nidulariales (bird's nest fungi) use a splash cup mechanism. In these cases the basidiospore typically lacks a hilar appendage, and no forcible discharge occurs. Each example is thought to represent an independent evolutionary loss of the forcible discharge mechanism ancestral to all basidiomycetes.


* Ingold, C.T. 1998. Ballistosporic basidia. The Mycologist 12:50-52.
* Ingold, C.T. 1991. A view of the active basidium in heterobasidiomycetes. Mycological Research 95:618-621.
* Money, N.P. 1998. More g’s than the Space Shuttle: ballistospore discharge. Mycologia 90:547-558.
* Pringle, A., S.N. Patek, M. Fischer, J. Stolze, and N.P. Money. 2005. The captured launch of a ballistospore. Mycologia 97:866-871.

External links

* [ How do fungi reproduce?]
* [ APSnet Illustrated Glossary of Plant Pathology: Basidum]
* [ "Basidiomycota"] by Koenraad Muylaert, in Dutch
* [ Demonstrating basidiospore discharge] by John Webster. Mycological Society of America Lab Manual
* [ IMA Mycological Glossary: Basidum]
* [ Spore discharge and dispersal in mushrooms] by Heino Lepp, Australian National Botanic Gardens.
* [ "Using a Microscope: Basidia and Cystidia"] by Michael Kuo, ""

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  • Basidium — Ba*sid i*um, n. [NL., dim. of Gr. ba sis base.] (Bot.) A special oblong or pyriform cell, with slender branches, which bears the spores in that division of fungi called Basidiomycetes, of which the common mushroom is an example. [1913 Webster] …   The Collaborative International Dictionary of English

  • basidium — basidium. См. базидий. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • basidium — [bə sid′ē əm] n. pl. basidia [bə sid′ēə] [ModL < Gr basis,BASIS + ModL dim. suffix idium] Bot. any of a number of oblong cells in basidiomycetous fungi, bearing a definite number of external spores (usually four) on short, slender stalks… …   English World dictionary

  • Basidium — Basidien (Singular: Basidie oder Basidium) sind die Meiosporangien der Basidienpilze (Basidiomycota). Wie bei den Asci der Schlauchpilze (Ascomycetes) gibt es auch bei den Basidien unterschiedliche Formen. Die Sporen, die an Basidien entstehen,… …   Deutsch Wikipedia

  • basidium — basidial, adj. /beuh sid ee euhm/, n., pl. basidia / sid ee euh/. Mycol. a special form of sporophore, characteristic of basidiomycetous fungi, on which the sexual spores are borne, usually at the tips of slender projections. [1855 60; BAS(IS) +… …   Universalium

  • basidium — noun (plural basidia) Etymology: New Latin, from Latin basis Date: 1859 a structure on a basidiomycete in which karyogamy occurs followed by meiosis to form usually four basidiospores …   New Collegiate Dictionary

  • basidium — (bah sid e um; pl., basidia) A structure that bears on its surface a definite number of basidiospores (typically four) that are formed following karyogamy and meiosis. Basidia are found in the basidiomycetes and are usually club shaped …   Dictionary of microbiology

  • basidium — Club shaped organ involved in sexual reproduction in basidiomycete fungi (mushrooms, toadstools etc.). Bears four haploid basidiospores at its tip …   Dictionary of molecular biology

  • basidium — noun A small structure, shaped like a club, found in the Basidiomycota division of fungi, that bears four spores at the tips of small projections …   Wiktionary

  • basidium — A cell or spore bearing organ usually club shaped that is characteristic of the Basidiomycota. It bears basidiospores externally after karyogamy and meiosis. It is composed of a swollen terminal cell situated on a slender stalk, and gives rise to …   Medical dictionary

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