Editing Basidium

{{Short description|Fungal structure}}
{{For|the fictional moon in novels by Eleanor Cameron|Mushroom Planet}}
{{more footnotes|date=March 2013}}
[[File:Basidium schematic.svg|thumb|right|500px|Diagram showing a basidiomycete mushroom, gill structure, and spore-bearing basidia on the gill margins.]]

A '''basidium''' ({{plural form}}: '''basidia''') is a microscopic [[spore]]-producing structure found on the [[hymenophore]] of [[sporocarp (fungi)|reproductive bodies]] of [[Basidiomycota|basidiomycete]] fungi. The presence of basidia is one of the main characteristic features of the group. These bodies are also called tertiary [[mycelium|mycelia]], which are highly coiled versions of secondary mycelia. A basidium usually bears four sexual spores called [[basidiospores]]. Occasionally the number may be two or even eight. Each reproductive spore is produced at the tip of a narrow prong or horn called a [[sterigma]] ({{plural form|sterigmata}}), and is forcefully expelled at full growth.

The word ''basidium'' literally means "little pedestal". This is the way the basidium supports the spores. However, some biologists suggest that the structure looks more like a [[club (weapon)|club]]. A partially grown basidium is known as a '''basidiole'''.

==Structure==
Most [[basidiomycota]] have single celled basidia ('''holobasidia'''), but some have ones with many cells (a  '''phragmobasidia'''). For instance, [[Rust (fungus)|rust fungi]] in the order ''Puccinales'' have phragmobasidia with four cells that are separated by walls along their cross section. Some jelly fungi in the order [[Tremellales]] also have phragmobasidia with four cells that are separated by walls and are shaped like a cross. Sometimes the basidium develops from a '''probasidium''', which is not elongated like a typical [[hypha]]. The basidium may be stalked or attached directly to the hyphae{{cn|date=February 2025}}.

The basidium is normally [[Club (weapon)|club]]-shaped: narrow at the stem and wide near its outer end. It is widest in the middle hemispherical dome at its apex, and its base is about half the size of the widest diameter at the highest point. Basidia with a short and narrow base are shaped like an inverted egg, and occur in genera such as ''[[Paullicorticium]]'', ''[[Oliveonia]]'', and ''[[Tulasnella]]''. Basidia with a wide base are often shaped like a barrel.<ref name="Donk 1963"/>

==How basidiospores are expelled==
In most [[basidiomycota]], the basidiospores are forcibly expelled. 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 drop of fluid that builds up at the nearer tip ('''hilar appendage''') of each basidiospore; the offset attachment of the spore to the extending narrow prong, and the presence of [[hygroscopic]] regions on the basidiospore surface. Basidiospore discharge can only succeed after sufficient water vapor has condensed on the spore.

When a basidiospore matures, sugars present in the cell wall begin to serve as condensation loci for water vapour 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 builds up as a large, almost spherical water droplet.

[[File:03 01 04 discharge of ballistospore (M. Piepenbring).png|thumb|upright=1.2|right]]

At the same time, condensation occurs in a thin film on the stalk-facing part of the spore. When these two bodies of water combine, the release of surface tension and the sudden change in the center of gravity suddenly expels the basidiospore. Remarkably, the initial acceleration of the spore is estimated to be about 10,000&nbsp;[[Standard gravity|{{mvar|g}}]].<ref name=Money-1998/>

===Evolutionary loss of expulsion by force===
Some basidiomycetes do not have a means to forcibly expel their basidiospores, although they still form them. In each of these groups, spore dispersal occurs through other means of expulsion.{{cn|date=February 2025}}

For example:
* Members of the order Phallales ([[stinkhorns]]) rely on insect [[dispersal vector|vectors for dispersal]].{{cn|date=February 2025}}
* The dry spores of the [[Lycoperdales]] ([[puffball]]s) and [[Sclerodermataceae]] (earth balls and kin) are dispersed when the basidiocarps are disturbed.{{cn|date=February 2025}}
* Species of the [[Nidulariales]] (bird's nest fungi) use a splash cup mechanism.{{cn|date=February 2025}}

In these cases the basidiospore typically lacks a hilar appendage, and expulsion by force does not occur. Each example is thought to represent an independent evolutionary loss of the forcible discharge that comes before all basidiomycetes.{{cn|date=February 2025}}

==References==
{{Reflist|refs=

<ref name="Donk 1963">
{{cite journal
 |author=Donk, M.A.
 |year=1963
 |title=A conspectus of the families of Aphyllophorales
 |journal=Persoonia
 |volume=3  |issue=3  |page=214
 |url=http://www.cybertruffle.org.uk/cyberliber/61056/0003/002/0214.htm
}}
</ref>

<ref name=Money-1998>
{{cite journal
 |author=Money, N.P.
 |year=1998
 |title=More {{mvar|g}}'s than the Space Shuttle: Ballistospore discharge
 |journal=Mycologia
 |volume=90  |issue=4
 |pages=547–558
|doi=10.1080/00275514.1998.12026942
 }}
</ref>

}} <!-- end "refs=" -->

:* {{cite journal
 |author=Ingold, C.T.
 |year=1998
 |title=Ballistosporic basidia
 |journal=The Mycologist
 |volume=12  |issue=2
 |pages=50–52
|doi=10.1016/S0269-915X(98)80040-2
 }}

:* {{cite journal
 |author=Ingold, C.T.
 |year=1991
 |title=A view of the active basidium in heterobasidiomycetes
 |journal=Mycological Research
 |volume=95  |issue=5
 |pages=618–621
|doi=10.1016/S0953-7562(09)80076-2
 }}

:* {{cite journal
 |author1=Pringle, A.  |author2=Patek, S.N.
 |author3=Fischer, M.  |author4=Stolze, J.
 |author5=Money, N.P.
 |year=2005
 |title=The captured launch of a ballistospore
 |journal=Mycologia
 |volume=97  |issue=4
 |pages=866–871
|doi=10.1080/15572536.2006.11832777
 |pmid=16457355
 |s2cid=218586848
 }}

==External links==
* [http://americanmushrooms.com/basics.htm#Reproduction AmericanMushrooms.com: How do fungi reproduce?]
* [https://web.archive.org/web/20060927231933/http://www.apsnet.org/education/IllustratedGlossary/PhotosA-D/basidium.htm APSnet Illustrated Glossary of Plant Pathology: Basidum]
* [https://web.archive.org/web/20070928180413/http://carroll1.cc.edu/~jclausz/msamanual/ballistospore.html Demonstrating basidiospore discharge] by John Webster. Mycological Society of America Lab Manual
* [http://www.mushroomthejournal.com/greatlakesdata/Terms/basid133.html IMA Mycological Glossary: Basidum]
* [http://www.anbg.gov.au/fungi/spore-discharge-mushrooms.html Spore discharge and dispersal in mushrooms] by Heino Lepp, Australian National Botanic Gardens.
* [http://www.mushroomexpert.com/microscope_cystidia.html "Using a Microscope: Basidia and Cystidia"] by Michael Kuo, ''MushroomExpert.com''
{{Fungus structure}}

[[Category:Basidiomycota]]
[[Category:Fungal morphology and anatomy]]