Basidiomycetes

 

Roughly 25,000 species of fungi are classified in the phylum Basidiomycota.  Basidiomycetes or club fungi as they are more commonly called are important decomposers of wood and other plant material.  Of all fungi there is none better at decomposing the complex polymer lignin, an abundant component of wood, than saprobic basidiomycetes.  Some form mycorrhizae with plants while other groups such as rusts and smuts include particularly destructive plant parasites (Campbell, 624) that attack crops like wheat (Tree of Life, http://tolweb.org/tree?group=fungi).   Furthermore, certain species form symbiotic associations with insects like leaf-cutter ants and termites.  In addition to being found in practically every terrestrial ecosystem, basidiomycetes are also found in both freshwater and marine habitats (Tree of Life, http://tolweb.org/tree?group=fungi).

 

Basidiomycetes are capable of reproducing both asexually and sexually.  Their life cycle frequently contains a long-lived mycelium that will in response to environmental stimuli reproduce sexually by producing Amanita flavoconiaelaborate fruiting bodies called basidiocarps.  A common example of a basidiocarp is a mushroom.  The gills, which are located underneath the cap of the mushroom, produce up to a billion spores that drop beneath the cap and are blown away by wind (Campbell, 624).  In contrast to this everyday method of spore dispersal is the production and forcible discharge of ballistospores by various species.  In this form of spore discharge, the ballistospore is discharged by a mechanism referred to as “surface tension catapult”.  In this form of spore dispersal the ballistospores are expelled from basidia, hyphae, yeast cells, or other ballistospores with a force of approximately 25,000 g (Tree of Life, http://tolweb.org/tree?group=fungi).

 

Basidiomycetes concentrate growth primarily in the hyphae of a mushroom.  Such concentrated growth allows basidiomycete mycelium to create the fruiting structures in just a few hours (Campbell, 624). 

 

The Basidiomycetes, or club fungi, produce sexual spores (basidiospores) externally on a club-shaped structure called a basidium (Barron, 86).  Generally speaking, each basidium produces four spores on the tips of minute stalks called sterigmata.  It is from this reproductive structure (basidium) that the group takes its name (Tree of Life, http://tolweb.org/tree?group=fungi).

 

The Division Basidiomycota can be broken down into smaller groups called classes.  The following classes are outlined in more detail below: Gasteromycetes, Phragmobasidiomycetes and Hymenomycetes (Barron, 86).

 

Gasteromycetes

Rather than expelling their spores directly into the air Gasteromycetes (stomach fungi) produce their spores inside the fruitbodies.  Fungi in this group include puffballs, earthstars, bird’s nest fungi, and stinkhorns (Barron , 86).

 

Lycoperdon pyriforme

Puffballs come in a variety of shapes that include spherical, subspherical, ellipsoid, pestle-shaped, and pear-shaped.  Spores mature inside the fruitbody as a powdery mass.  The fruitbody itself is typically covered with spines that flake off to expose a smooth, membranous wall.  Species such as those found in the Lycoperdon genera have a distinct pore at the apex of the fruitbody.  When raindrops strike the outside of the fruitbody, the implosion of the wall forces a puff of spores into the air through the pore (Barron , 86).

 

Earthstars, aptly named because of their shape, are found underneath loose duff on the forest floor.  The star shape of the fungi is formed when the thick outer wall splits forming a number of pointed arm-like segments.  These segments reflex in response to drying out, which in turn exposes and raises a puffball-like spore sac above the ground for better spore dispersal.  Earthstar spore dispersal occurs in the same fashion as that of puffballs.  As raindrops strike the outside of the spore sac spores are “puffed” out a pore (Barron, 86).

 

Crucibulum laeveA Bird’s Nest Fungus, as one would expect, looks like a nest with eggs, but only on a much smaller scale.  The “eggs” (peridioles) within the nest are actually packages of thousands of tiny spores covered by a hard outer wall.  In various species of Bird’s Nest Fungus the eggs are anchored to the side of the wall by a structure that contains a thread-like tail (funiculus) and a sticky base (hapteron).  Raindrops are once again the driving force behind spore dispersal.  As raindrops fall into the “nest” the splash it causes the “egg(s)” to be ejected out of the cup whereupon they have the potential to attach to a suitable substrate via their sticky base (Barron, 86).

 

Stinkhorn fruitbodies resemble those of puffballs during the stage of development commonly referred to as the “egg stage”. Mutinus caninus During this period of growth the fruitbody is either spherical to subspherical or ellipsoid.  The egg consists of a gelatinous layer that surrounds an olive-green spore-mass, which in turn covers the head of the stinkhorn.  In Phallus and Mutinus spp. the head further surrounds a central column that upon maturity will form a support stalk.  When the fruitbody matures the gelatinous layer mixes with the spore-mass to produce a foul smelling olive-green goo after which the stinkhorn is named.  The fetid gooey spore mass attracts flies over large distances to feed on sugar materials contained within the gelatinous-spore mixture.  As the flies feed, spores contained in the mixture stick to the flies’ bodies and are in turn transported to other sites (Barron, 87).  

 

Phragmobasidiomycetes

Tremella lutescens

Better known as jelly fungi, Phragmobasidiomycetes have fruitbodies that are typically in a gelatinous matrix.  As the weather becomes dry jelly fungi dry out forming shriveled, irregular horny masses.  However, the fungus quickly revives and returns to its normal shape, size and color after it rains as the gelatin absorbs rainwater (Barron ,101).

 

 

Not all jelly fungi are clearly gelatinous.  There are several species that at first glance lookTremellodendron pallidum more like a coral fungus.  False Coral Fungus (Tremellodendron pallidum) for example, has fruitbodies that consist of a cluster of tightly packed branches that are tough, flattened, and dry.  Microscopically however it is related to jelly fungi.  One of the most effective ways of discerning between false and true coral fungus is to examine the structural integrity of the fruitbody.  True coral fungi have fruitbodies that are fragile, break easily and decay quickly as opposed to false coral fungi that have fruitbodies that are for the most part tough and persistent (Barron, 101).

 

In addition to jelly fungi that appear to not belong in the “jelly group” there are fungi that are not true jellies but appear to be.  Ascotremella faginea and Neobulgaria pura, which are sac fungi, mimic the true jellies by producing fruitbodies in a gelatinous matrix.  Microscopic examination of these two species reveals that the fruitbodies contain asci and not basidia (Barron, 101).

 

Hymenomycetes

 

The final class in the Division Basidiomycota is that of Hymenomycetes.  This group includes coral fungi, tooth fungi, bracket fungi, and boletes (Barron ,110).

 

Ramaria botrytis

Coral fungi typically have two basic fruitbody forms.  The simpler form, which is often referred to as Club Coral, is erect and unbranched appearing worm-like or clavate (club shaped).  A good example of this type of coral fungi is Worm-Like Coral (Clavaria vermicularis).  Frequently, however coral fungi do not produce fruitbodies that are worm-like or clavate but instead form coral-like masses.  Even though certain species of coral fungi are a dull brown, many range in color from white to tan or bright orange-yellow to rose or purple (Barron, 110).

 

Although many coral fungi are very attractive in appearance they can be very difficult to identify to species and even to genus at times.  Microscopic examination is often needed to separate one species from another.  While some species of coral fungi are good edibles there are species that produce gastrointestinal toxins such as Pink-Tipped Coral (Ramaria formosa).  The toxicity and difficulty in identification make coral fungi poor candidates for consumption (Barron, 110).

 

Certain species of club-shaped sac fungi and jelly fungi are very similar in appearance to the simple Club Coral fungi.  A quick examination of the fruitbody is typically all that is needed to determine if the fungus is a coral fungus or not.  The fruitbodies of coral fungi have a tendency to be soft, fragile, and brittle and decay rapidly.  On the other hand, sac fungi are tougher, more persistent and resistant to decay.  Similarly, the fruitbodies of jelly fungi are tough and persistent having the ability to revive in wet weather after drying out for months at a time (Barron, 110). 

 

Hydnum umbilicatumTooth fungi contain only a moderate sampling of macrofungi and are easily recognizable by the tooth-like spines that cover portions of the fruitbody.  Generally speaking tooth fungi are tough, woody and inedible.  However, certain species of Hydnum and Hericium are soft, fragile and highly prized edibles (Barron, 121).

 

Bracket fungi (or shelf fungi) grow on the sides of trees much like shelves hence their name.  They range in size from hefty and tough to small, thin, and fragile.  Not all bracket fungi however produce brackets.  Some tend to resemble mushrooms, in particular boletes, in that they have a cap with pores on the undersurface and central stalk.  Close examination however will reveal that these look-alikes are tough and leathery, which easily distinguishes them from soft, fleshy boletes.  In addition, some bracket fungi produce flat fruitbodies on the underside of a twig or branch instead of shelves on the sides of trees (Barron, 130). Typically, bracket fungi have fruitbodies that are tough and leathery or woody in texture.  The fruitbody consists of both thin-walled, living hyphae and thick-walled, dead hyphae.  The living hyphae functions to transport nutrients and produce spores while the dead hyphae contains branching fibers that interlock resulting in an exceptionally hard and rigid fruitbody.  Consequently, the fruitbodies have the ability to persist for long periods of time (Barron ,129).  Some have the ability to survive for weeks, months, or even years.  For example, Artist’s Conk can live for several years, producing a new layer of pores each year.   During the summer months brackets may drHemlock Varnishy up and shrink slightly as a result of heat and or drought.  Conversely, they have the ability to recover in periods of rain and start spore production again (Barron, 130). The undersides of bracket fungi have a perforated appearance and it is for this reason they are also called polypores.  The perforated appearance is a result of the underside of the fruitbody being lined by a series of tubes that are tipped with pores.  It is through these tubes and their pores that spores are released.  Pores come in a variety of shapes and sizes.  They may be as small as a fraction of a millimeter across up to almost one centimeter in diameter.  Their shapes include circular, angular, elongate, and labyrinth form (maze-like) (Barron,129). Most bracket fungi tend to dull and boring, but there are several that are very colorful and attractive.  For example, Chicken of the Woods (Laetiporus sulphureus) has bright sulphur-yellow to yellow-yellow orange brackets. Chicken of the Woods Cinnabar Polypore (Pycnoporus cinnabarinus) has brackets that are pale orange to cinnabar on the upper surface and brilliant-orange red underneath.  Also, Turkey Tail (Trametes versicolor) Turkey Tailhas a velvety fruitbody with tan to orange to red-brown to amber zonation (bands) (Barron, 130). Various fungi superficially resemble bracket fungi.  False Turkey Tail (Stereum ostrea) is probably the most commonly encountered look-alike, mimicking Turkey Tail.  These two species are easily distinguished by examining their undersides.  False Turkey Tail has no pores, whereas Turkey Tail has pores on its underside (Barron, 130). 

 

Boletes (Sponge Mushrooms) at first glance look like your typical gilled mushroom.  However, closer examination of the underside of the cap will reveal tubes instead of gills.  The tubes range in size from extremely shallow to more than a centimeter deep.  Birch BoleteThe end of the tube that opens to the exterior of the fruitbody appears as a pore.  Pores come in a number of shapes and sizes depending on the species.  Shapes of pores include circular, angular, labyrinth, radial, and irregular.  Size varies from over a centimeter across to so small that it is difficult to resolve the separation between two pores without a magnifying glass (Barron,156). Generally speaking most boletes are edible and many are considered highly prized edibles, for example King Bolete (Boletus edulis) is most delicious.  Nevertheless, care should be taken before eating any bolete.  Certain boletes such as Boletus satanas are poisonous, while others have such an aversive taste, such as Bitter Bolete (Tylopilus felleus), that they are unpalatable for most.  Last, but definitely not least, most fruitbodies of boletes have been attacked by insects before picking and consequently are riddled with insect larvae (Barron, 156). 

 

Amanitas

           

Amanita spp. form a group of mostly large and often colorful fungi that are ecologically important.  Their ecological significance is seen most prominently in their mychorrizal relationships with coniferous and hardwood trees (Barron, 234.) Typical features used in the identification of Amanita are (1) white spore print, (2) free gills, (3) cup at the base, (4) patches or warts scattered over tAmanita pantherinahe cap, and (4) a ring on the stem.  As is typical with most groups of fungi, various species of  Amanita do not posses each of the aforementioned features.  Other species may contain the feature only to loose it as it ages.  Nevertheless, with a little experience Amanita spp. become fairly easy to recognize (Barron, 234). Many species are highly regarded as prized edibles.  This however is not an invitation to sample unknown species.  Certain species of Amanita contain deadly toxins (amatoxins) which when ingested can lead to a painful death.  Even in small doses these toxins can cause irreversible damage to vital organs, in particular the liver and kidneys.  For these reasons, it is not recommended that you treat any species of Amanita as edible (Barron, 234). 

 

Works Cited

 

Barron, George.  Mushrooms of Northeast North America.  Edmonton: Lone Pine,
            1999.

 

Campbell, Neil A. Biology. 4th ed. Menlo Park: The Benjamin/Cummings Publishing

            Company, 1996.

 

Tree of Life Web Project.  2006.  The University of Arizona College of Agriculture and

            Life Sciences and The University of Arizona Library. 21 April 2006. 

            <http://tolweb.org/tree/>