Basidium

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Diagram showing a basidiomycete mushroom, gill structure, and spore-bearing basidia on the gill margins. Basidium schematic.svg
Diagram showing a basidiomycete mushroom, gill structure, and spore-bearing basidia on the gill margins.

A basidium (pl.: basidia) is a microscopic spore-producing structure found on the hymenophore of reproductive bodies of basidiomycete fungi. The presence of basidia is one of the main characteristic features of the group. These bodies also called tertiary 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 (pl. sterigmata), and is forcefully expelled at full growth.

Contents

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. 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 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.

The basidium is normally 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. [1]

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.

03 01 04 discharge of ballistospore (M. Piepenbring).png

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  g. [2]

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.

For example:

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.

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<span class="mw-page-title-main">Basidiomycota</span> Division of fungi

Basidiomycota is one of two large divisions that, together with the Ascomycota, constitute the subkingdom Dikarya within the kingdom Fungi. Members are known as basidiomycetes. More specifically, Basidiomycota includes these groups: agarics, puffballs, stinkhorns, bracket fungi, other polypores, jelly fungi, boletes, chanterelles, earth stars, smuts, bunts, rusts, mirror yeasts, and Cryptococcus, the human pathogenic yeast.

<span class="mw-page-title-main">Puffball</span> Fungus

Puffballs are a type of fungus featuring a ball-shaped fruit body that bursts on contact or impact, releasing a cloud of dust-like spores into the surrounding area. Puffballs belong to the division Basidiomycota and encompass several genera, including Calvatia, Calbovista and Lycoperdon. The puffballs were previously treated as a taxonomic group called the Gasteromycetes or Gasteromycetidae, but they are now known to be a polyphyletic assemblage.

The hymenium is the tissue layer on the hymenophore of a fungal fruiting body where the cells develop into basidia or asci, which produce spores. In some species all of the cells of the hymenium develop into basidia or asci, while in others some cells develop into sterile cells called cystidia (basidiomycetes) or paraphyses (ascomycetes). Cystidia are often important for microscopic identification. The subhymenium consists of the supportive hyphae from which the cells of the hymenium grow, beneath which is the hymenophoral trama, the hyphae that make up the mass of the hymenophore.

<span class="mw-page-title-main">Heterobasidiomycetes</span> Class of fungi

Heterobasidiomycetes, including jelly fungi, smuts and rusts, are basidiomycetes with septate basidia. This contrasts them to homobasidiomycetes, including most mushrooms and other Agaricomycetes, which have aseptate basidia. The division of all basidiomycetes between these two groups has been influential in fungal taxonomy, and is still used informally, but it is no longer the basis of formal classification. In modern taxonomy homobasidiomycetes roughly correspond to the monophyletic class Agaricomycetes, whereas heterobasidiomycetes are paraphyletic and as such correspond to various taxa from different taxonomic ranks, including the Basidiomycota other than Agaricomycetes and a few basal groups within Agaricomycetes.

<span class="mw-page-title-main">Basidiospore</span> Reproductive structure of a fungus

A basidiospore is a reproductive spore produced by basidiomycete fungi, a grouping that includes mushrooms, shelf fungi, rusts, and smuts. Basidiospores typically each contain one haploid nucleus that is the product of meiosis, and they are produced by specialized fungal cells called basidia. Typically, four basidiospores develop on appendages from each basidium, of which two are of one strain and the other two of its opposite strain. In gills under a cap of one common species, there exist millions of basidia. Some gilled mushrooms in the order Agaricales have the ability to release billions of spores. The puffball fungus Calvatia gigantea has been calculated to produce about five trillion basidiospores. Most basidiospores are forcibly discharged, and are thus considered ballistospores. 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.

<i>Stereum sanguinolentum</i> Species of fungus

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A ballistospore or ballistoconidia is a spore that is discharged into the air from a living being, usually a species of fungus. With fungi, most types of basidiospores formed on basidia are discharged into the air from the tips of sterigmata. At least 30 thousand species of mushrooms, basidiomycete yeasts, and other fungal groups may discharge ballistospores, sometimes at initial accelerations exceeding 10 thousand times g.

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<span class="mw-page-title-main">Hydnaceae</span> Family of fungi

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<i>Crucibulum</i> (fungus) Genus of fungi

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<i>Nidula</i> Genus of fungi

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<i>Cyathus stercoreus</i> Species of fungus

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<span class="mw-page-title-main">Nidulariaceae</span> Family of fungi

The Nidulariaceae are a family of fungi in the order Agaricales. Commonly known as the bird's nest fungi, their fruiting bodies resemble tiny egg-filled birds' nests. As they are saprobic, feeding on decomposing organic matter, they are often seen growing on decaying wood and in soils enriched with wood chips or bark mulch; they have a widespread distribution in most ecological regions. The five genera within the family, namely, Crucibulum, Cyathus, Mycocalia, Nidula, and Nidularia, are distinguished from each other by differences in morphology and peridiole structure; more recently, phylogenetic analysis and comparison of DNA sequences is guiding new decisions in the taxonomic organization of this family.

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Marasmius funalis is a species of Marasmiaceae fungus known only from Japan. The species produces small mushrooms with reddish-brown caps up to 6 millimetres (0.24 in) in diameter and dark-brown, threadlike stems of up to 50 millimetres (2.0 in) in length. The species has a number of distinctive microscopic features, including very long cystidia on the stem, visible as bristles. Described in 2002 by Haruki Takahashi, the species grows on dead wood. The closest relative of M. funalis is M. liquidambari, known from Mexico and Papua New Guinea, and it is also similar in appearance to M. hudonii and Setulipes funaliformis, the latter of which was named after M. funalis.

<i>Mycena chlorophos</i> Species of agaric fungus in the family Mycenaceae

Mycena chlorophos is a species of agaric fungus in the family Mycenaceae. First described in 1860, the fungus is found in subtropical Asia, including India, Japan, Taiwan, Polynesia, Indonesia, and Sri Lanka, in Australia, and Brazil. Fruit bodies (mushrooms) have pale brownish-grey sticky caps up to 30 mm (1.2 in) in diameter atop stems 6–30 mm (0.2–1.2 in) long and up to a millimeter thick. The mushrooms are bioluminescent and emit a pale green light. Fruiting occurs in forests on fallen woody debris such as dead twigs, branches, and logs. The fungus can be made to grow and fruit in laboratory conditions, and the growth conditions affecting bioluminescence have been investigated.

Chionosphaera is a genus of fungi in the family Chionosphaeraceae. It has four species.

References

  1. Donk, M.A. (1963). "A conspectus of the families of Aphyllophorales". Persoonia. 3 (3): 214.
  2. Money, N.P. (1998). "More g's than the Space Shuttle: Ballistospore discharge". Mycologia. 90 (4): 547–558. doi:10.1080/00275514.1998.12026942.