Classification of Mushrooms & Other Fungi

Fungi are more closely related to animals than to plants. Although fungi resemble plants because they generally remain in one place, their evolutionary lineage is closer to that of animals.

Fungi and plants occupy different major branches of the eukaryotic family tree. Eukaryotes are organisms whose cells contain nuclei, distinguishing them from bacteria and archaea. The classification presented divides them into Bikonta, which includes plants and algae, and Amorphea, historically associated with the term Unikonta, which includes animals and fungi.

The names Bikonta and Unikonta refer to the flagella of ancestral cells. The terms distinguish lineages historically associated with two flagella and one flagellum, respectively. Flagella are tail-like structures used by certain cells for movement.

Two familiar forms of mold are not actually fungi. Water molds belong to the oomycete lineage, while slime molds such as those in Myxogastria belong to a separate evolutionary group. Their resemblance to fungi does not mean they share the same classification.

The organism responsible for the Irish potato blight was a water mold. Potato blight contributed to the Great Irish Famine of the mid-19th century, making it a historically important example of a fungus-like organism outside the fungal kingdom.

Some slime molds appear as bright yellow, spongy growths on trees. These organisms can develop on bark and decaying wood and are frequently mistaken for ordinary fungi.

Fungi are classified through a hierarchy of seven principal taxonomic ranks. These are kingdom, phylum, class, order, family, genus, and species. Scientific species names combine the genus and species designation, conventionally written in italics.

The fuzzy gray mold that develops on forgotten bread belongs to the pin-mold group. These fungi are associated with Mucoromycotina and appear under magnification as networks of fine, pale threads bearing dark reproductive structures.

The main body of most fungi is a network called mycelium. Individual fungal threads are known as hyphae. Together, they form the mycelium, which constitutes the principal body of many fungal organisms.

The visible mushroom is usually only the reproductive structure of a much larger fungus. Most of the organism exists as mycelium in soil, wood, or another growing medium. The familiar mushroom is a fruiting body produced by that network.

A mushroom is more comparable to a plant's fruit than to its roots. The mycelium performs many of the functions required to sustain the fungus, while the mushroom is a specialized reproductive structure.

Most higher fungi belong to two major phyla: Basidiomycota and Ascomycota. Basidiomycota are commonly called club fungi, while Ascomycota are called sac fungi. These names reflect differences in their reproductive structures.

The scientific study of fungi is called mycology. Many fungal classification names contain elements derived from the Greek word for fungus, explaining the repeated appearance of terms such as myco and mycetes.

Smut fungi are agricultural parasites that attack economically important crops. Members of Ustilaginomycetes commonly infect grasses, including wheat, rice, and corn. Their importance comes partly from the damage they can cause to food production.

Jelly fungi include the organism commonly called witch's butter. These fungi have soft, gelatinous fruiting bodies and are frequently found growing on bark or decaying wood. They are represented in the classification by Tremellomycetes.

Rust fungi are another major group of agricultural parasites. Members of Pucciniomycetes commonly infect plant leaves, producing discoloration and growths resembling rust.

Most familiar mushrooms belong to the class Agaricomycetes. This group contains many of the mushrooms recognizable from forests, gardens, and food markets, although its members have considerably more diverse shapes than the conventional cap-and-stem mushroom.

The familiar mushroom with a cap, stem, and gills is called an agaric. Agarics represent only one form of fungal fruiting body. Other mushrooms may lack stems, lack gills, or have entirely different structures.

Shelf fungi grow outward from trees rather than rising from the ground on stems. These fungi, including members of Polyporales, form shelf-like structures attached to trunks and branches.

Boletes resemble conventional mushrooms but have pores instead of gills. Members of Boletales generally have caps and stems. Some species are edible, while others are poisonous.

Wild mushroom identification is dangerous because edible and poisonous species can look extremely similar. Baker emphasizes that the classification chart is not an identification guide and warns against eating wild mushrooms without expert knowledge.

Earthstars belong to the order Geastrales. Their outer layers spread outward into star-like formations, giving these mushrooms their distinctive appearance and common name.

Stinkhorn mushrooms use their unpleasant smell to attract insects that disperse spores. Members of Phallales often have unusually shaped fruiting bodies and produce odors that attract flies, which help spread their reproductive material.

Tooth fungi have small tooth-like structures instead of conventional gills. They are discussed among the mushrooms associated with Cantharellales, illustrating how fungal reproductive surfaces can differ.

Chanterelles are yellow-to-orange mushrooms valued in cooking. These fungi, associated with Cantharellales, are particularly familiar from French cuisine.

Milk-cap mushrooms release a milk-like liquid when damaged. Members of the genus Lactarius are named for the latex-like substance that can emerge from their gills.

Brittlegills belong to the genus Russula and include species with striking red caps. Their appearance can resemble other mushrooms, including the famous fly agaric, making visual identification potentially misleading.

Agaricales is the largest order discussed within Agaricomycetes. It contains many of the familiar gilled mushrooms, including important edible and poisonous species. Two especially notable families are Amanitaceae and Agaricaceae.

The genus Amanita contains both some of the world's most dangerous mushrooms and edible species. Baker illustrates seven species from the genus, showing why membership in a familiar mushroom group provides no assurance of safety.

The fly agaric, Amanita muscaria, is one of the most recognizable mushrooms in popular culture. Its red cap with white spots has influenced mushroom imagery in the Super Mario games, the Smurfs, Disney's Fantasia, and traditional depictions of fairies and gnomes.

Fly agarics were historically used to repel flies. According to the account, people in medieval times cut their caps into pieces and mixed them with milk to attract or control flies, giving the mushroom its common name.

The white spots on fly agaric caps are remnants of a protective veil. Young Amanita mushrooms develop inside a covering that breaks apart as the mushroom expands. Pieces of the original covering can remain attached to the cap.

The ring around the stem of many agarics is also the remnant of a protective veil. A separate membrane initially covers the developing gills and later tears as the cap opens, sometimes leaving a ring around the stem.

Fly agarics are poisonous but are generally less lethal than certain related Amanita species. Their striking appearance should not be confused with safety, particularly because toxicity varies significantly across the genus.

The death cap, Amanita phalloides, is responsible for a large proportion of fatal mushroom poisonings. It contains extremely dangerous toxins, and even relatively small quantities can cause fatal poisoning. Baker stresses the possibility of death within days of consumption.

Destroying angels are another exceptionally dangerous group of Amanita mushrooms. They include Amanita bisporigera and related species, which are known for their severe toxicity.

Caesar's mushroom, Amanita caesarea, is an edible species historically associated with Roman emperors. It grows primarily in parts of Europe, including Italy, and was reportedly favored by Roman rulers.

Amanita jacksonii is a North American mushroom resembling Caesar's mushroom. Its similarity illustrates how related species can occupy different geographic regions while sharing recognizable features.

The most widely consumed cultivated mushroom belongs to the species Agaricus bisporus. Button mushrooms and portobello mushrooms are different commercial forms of the same species.

The genus Agaricus also includes almond mushrooms, horse mushrooms, and meadow mushrooms. Some are known for distinctive flavors, such as the almond-like taste associated with almond mushrooms, while others commonly occur in grassy fields.

Yellow stainers are poisonous relatives of familiar edible Agaricus mushrooms. They are named for the yellow discoloration that appears when their tissues are cut or bruised. Their resemblance to edible mushrooms reinforces the risks of identification by appearance alone.

The shaggy ink cap is also known as the lawyer's wig. Its elongated, shaggy appearance resembles an old-fashioned powdered wig, making it one of the more visually distinctive mushrooms discussed.

Parasol mushrooms resemble miniature umbrellas. Their broad caps and slender stems give them their name, and the ring left by the protective veil can be particularly visible.

Puffballs release clouds of spores when disturbed. Mature specimens can emit a visible powdery cloud when stepped on or compressed. Puffballs range from relatively small species to giant forms classified in different genera.

Mower's mushrooms become especially noticeable after lawns are cut. These small brown agarics belong to a group associated with Bolbitiaceae and commonly appear in grass.

Psilocybe cubensis contains the psychoactive compound psilocybin. Commonly called magic mushrooms or shrooms, these fungi are associated with hallucinogenic and psychedelic experiences. They are classified within Hymenogastraceae.

Oyster mushrooms belong to the family Pleurotaceae. They are among the best-known edible mushrooms outside the familiar button-mushroom group.

Shiitake mushrooms are classified within Omphalotaceae. They are an important cultivated edible mushroom and one of the prominent culinary examples discussed.

Enoki mushrooms belong to the family Physalacriaceae. Alongside oyster and shiitake mushrooms, they are identified as among the more familiar edible mushrooms after button mushrooms.

Waxcaps belong to the family Hygrophoraceae. Baker places them among the additional mushroom families represented in Agaricales and describes the examples shown as inedible.

Splitgill mushrooms resemble miniature shelf fungi. Members of Schizophyllaceae grow in small, shelf-like forms despite belonging to the order Agaricales.

Fairy rings occur when mushrooms emerge in a circular pattern from a shared fungal network. Species associated with Marasmiaceae can produce these formations. The mushrooms in such a ring may be reproductive structures of a single underground fungal organism rather than separate individuals.

Fairy rings demonstrate why the visible mushroom should not be treated as the entire organism. A spreading mycelium can produce fruiting bodies at different points around its perimeter, creating the appearance of multiple mushrooms growing in a circle.

Coral fungi are classified among Agaricales despite looking unlike ordinary agarics. Members of Clavariaceae develop branching structures resembling underwater coral rather than conventional caps and gills.

DNA sequencing has changed the classification of coral fungi. Their unusual appearance previously led to their placement elsewhere in fungal classification. Genetic evidence subsequently established relationships with members of Agaricales that were not obvious from their physical appearance.

Ascomycota includes most of the yeasts, many molds, lichens, mildews, and several unusual mushrooms. The group demonstrates that fungal diversity extends far beyond the familiar mushrooms found in forests or sold as food.

True yeasts differ from most fungi because they are generally single-celled. Rather than forming the extensive filament networks typical of many other fungi, they commonly reproduce through processes that produce genetically similar cells.

The true yeasts discussed belong to Saccharomycetes and Saccharomycetales. One of their principal families is Saccharomycetaceae. The repeated root saccharo refers to sugar.

Yeasts are closely associated with the fermentation of sugars. Their ability to metabolize sugars makes them important in food production, particularly baking and brewing.

Saccharomyces cerevisiae is commonly known as baker's yeast or brewer's yeast. In breadmaking, its fermentation produces carbon dioxide, creating gas pockets that expand the dough and cause bread to rise.

Candida is a medically important group of yeasts. Certain Candida species can cause infections in humans, illustrating that fungi include organisms associated with human disease as well as food production.

Many of the remaining ascomycete groups discussed belong to Pezizomycotina. This subdivision includes numerous molds, lichen-forming fungi, and species that produce conspicuous fruiting bodies.

Lichens are partnerships between fungi and photosynthetic organisms. They generally consist of a fungus associated with an alga or cyanobacterium, forming a combined biological structure through symbiosis.

Lichens are classified according to their fungal partner. Although multiple organisms participate in the association, the fungal component determines the lichen's placement in fungal taxonomy.

Crustose lichens grow in tightly attached, crust-like forms. Caloplaca is presented as an example, associated with the family Teloschistaceae and order Teloschistales.

Foliose lichens have leaf-like structures. Parmelia, also known among the shield lichens, can grow on older trees and form gray, flaky growths. It belongs to Parmeliaceae within Lecanorales.

Fruticose lichens develop branching or hanging structures. Usnea, commonly called old man's beard, often hangs from tree branches and resembles strands of hair or miniature branching vegetation.

Penicillium is responsible for familiar green molds and played a central role in the discovery of antibiotics. In 1928, an accidental observation showed that a Penicillium mold inhibited bacterial growth, helping establish the basis for penicillin.

The discovery associated with Penicillium transformed the treatment of bacterial infections. It led to the development of penicillin, the pioneering antibiotic that made many bacterial diseases treatable.

Penicillium molds are also used in cheesemaking. They contribute to the production of blue cheeses, where fungal growth is visibly present, and cheeses such as Brie, where the mold has a different appearance.

Aspergillus oryzae is an important fungus in Japanese food production. It is used in fermentation processes involved in making sake, miso, and soy sauce.

Penicillium and Aspergillus are classified within Aspergillaceae. This family belongs to the order Eurotiales and the class Eurotiomycetes, which contains several economically important molds.

Mold and mildew are commonly distinguished by their appearance. Baker describes mold as generally darker, thicker, and fuzzier, while mildew is typically paler and powdery, often appearing white, light gray, or beige.

Powdery mildew is a common fungal disease of plants. The genus Erysiphe, within Erysiphaceae and Erysiphales, includes fungi that infect leaves and produce recognizable powdery growths.

Cup fungi belong to the order Pezizales. Members of Pezizaceae form reproductive structures resembling small cups or bowls, demonstrating a distinct alternative to the familiar gilled mushroom.

True truffles belong to the family Tuberaceae and the genus Tuber. Unlike conventional aboveground mushrooms, their fruiting bodies develop underground.

Truffles are valuable because many edible species are relatively uncommon and difficult to obtain. Their underground growth and limited availability contribute to their often high market prices.

Morels belong to the family Morchellaceae. They are edible mushrooms distinguished by tall, honeycomb-like caps and are another type of fungus that can command high prices.

Orange peel fungus resembles pieces of discarded orange peel. This edible cup fungus belongs to Pyronemataceae, although Baker notes that its flavor is generally considered unimpressive.

Earth tongues are dark fungi that resemble tongues emerging from the ground. Members of the genus Geoglossum have black, elongated fruiting bodies and are classified within their own distinctive taxonomic group.

The genus Xylaria contains several fungi named for their resemblance to human or animal remains. Its unusual fruiting bodies illustrate the considerable variety of forms found within Ascomycota.

Dead man's fingers are named for their resemblance to blackened fingers protruding from the ground. The species is associated with the genus Xylaria and belongs to the family Xylariaceae.

Dead mole's fingers are another unusually shaped Xylaria fungus. Their appearance gives the impression of small dark fingers emerging from soil or decaying material.

Candlestick fungus, Xylaria hypoxylon, resembles miniature branching antlers. Its upright structures distinguish it from the thicker forms of other Xylaria species.

Xylaria belongs to the order Xylariales within Sordariomycetes. This class also contains Hypocreales, an order encompassing several additional fungi with distinctive ecological and practical importance.

Lobster mushrooms are edible fungi with a conspicuous orange appearance. They are associated with Hypocreaceae and are described as relatively large mushrooms that people commonly eat.

Caterpillar mushrooms are smaller orange fungi associated with Cordycipitaceae. They are described as edible but less commonly consumed than familiar culinary mushrooms.

Ergot is a fungus that causes disease in cereal grains. It belongs to Clavicipitaceae within Hypocreales and is another example of fungi with direct consequences for agriculture.

Ergot also has an important connection to psychedelic chemistry. Certain ergot fungi produce compounds related to lysergic acid, which can be used in the synthesis of LSD. This makes ergot notable both as an agricultural pathogen and as a source of medically and chemically significant substances.

The classification demonstrates that mushrooms, molds, yeasts, lichens, and crop pathogens are all connected through fungal evolution. Their different appearances and biological roles reflect substantial diversity within the fungal kingdom, while genetic classification helps establish relationships that cannot always be recognized from appearance alone.