Agaricomycetes - Pezizomycetes - Lecanoromycetes - Leotiomycetes - Arthoniomycetes
Fungi have cell walls and mainly live as saprobes, parasites, or in other symbiotic relationships. Flagella are usually absent except in spores of some simple types, which grow into enlarged cells with rhizoids. Most others form masses of filaments called hyphae that penetrate and absorb nutrients from the medium, though there are also some like yeasts that have reverted back to single cells.
These are part of the Basidiomycota, which during sexual reproduction form spores on the outside of cells called basidia. These typically develop into septate hyphae, which fuse to form a dikaryon containing a mix of nuclei from two or more parents. This is usually the main stage; for the most part diploid nuclei only occur during spore formation.
Agaricomycetes usually form large fruiting bodies like mushrooms. They mainly include types with club-shaped and non-septate basidia, though some are exceptions, often on external structures like spines, tubes, or lamellae. They are most notable as saprobes and for mycorrhizal associations with plants, where they provide water and minerals to roots in exchange for sugars.
A variety of pigments are found here, notably carotenoids and terphenyls. The most common of the former are β- and γ-carotene, also typical of related classes like jelly fungi. Canthaxanthin is typical of some bright orange Cantharellus (chanterelles), while Clathrus and several other stinkhorns have red colours from lycopene.
Terphenyls and their derivatives are a broad group of compounds derived as dimers of amino acids, usually tyrosine, which gives rise to atromentin and through it most others. Atromentin is itself accumulated as a brown pigment in some types and causes a violet colour change when they are treated with alkali.
Thelephorales and Polyporales are united mainly by genetic trees. These include many of the mushrooms with basidia on spine-like projections, and polypores, where they are in tubes on the underside of a tough fruiting body with an eccentric or no stalk. Some also form smooth crusts on wood, and a few are agarics, with a central stalk and basidia on distinct lamellae.
Terphenyls are common pigments in both these groups. Atromentin is found in Thelephorales such as Hydnellum aurantiacum, which get their colour from it and its red dibenzoate aurantiacin. Thelephoric acid, a widespread violet derivative, is also a typical component in this order and causes the flesh to turn blue or green in alkali.
Polyporales also have thelephoric acid or related compounds on occasion, for instance bright blue Terana caerulea with pigments derived from similar hydroquinones. Several others have phenylalanine-derived terphenyls, notably brown polyporic acid in genera like Hapalopilus, where it can make up as much as 40% of their dry weight.
Still other genera have entirely different pigments. The edible Laetiporus sulphureus (sulfur polypores) get their orange-yellow colour from laetiporic acid and related polyenes like the one shown. Another type occurs in Pycnoporus, which have red-orange cinnabarin and other phenoxazines.
Russulales are another genetic group with some polypores, spined fungi, and agarics, though they usually share some features like spore ornamentation. Special hyphae and cells with resinous or granular contents are very common here; they are best known in Lactarius (milk caps), which exude milky latex when injured.
These produce a variety of C15 terpenes, often in the form of esters that are broken down as an activated defense in damaged tissue. The most common is stearoylvelutinal, which gives rise to different pungent dialdehydes like isovelleral and velleral from L. vellereus, L. rufus, and various others. This serves to deter both herbivores and microbes.
Milk caps with coloured juice are generally edible cooked, though the terpenes still deter some bacteria at least. L. indigo gets its blue colour from stearoyldeterrol, and a reduced form is the orange-yellow in relatives like L. deliciosus. These break down to give purple lactaroviolin, and in the latter also blues like lactarazulene and yellows, so that they develop green bruises.
Boletales make up the boletes and their allies, most of which live in mycorrhizal associations with trees. The fruiting bodies in boletes are stalked, fleshy mushrooms where spores are discharged from tubes rather than ridges or lamellae. Some agarics and false truffles also belong here, as well as the dark sack-like earth-balls.
The main pigments here are terphenyl derivatives, especially pulvinic acids. Variegatic acid and its air-oxidized form variegatorubin are common types responsible for the yellowish and red colours in many genera. Some Boletus and Suillus also oxidize these acids to quinone methides when cut or bruised, turning the flesh bluish.
Several other genera turn bluish or brownish on injury from oxidation of cyclopentanoid derivatives, for instance colourless involutin in Paxillus involutus (brown roll-rims). Besides these types many Suillus have orange-red grevillins, formed by a related but different pathway from terphenyls, and some others have pigments derived from quinones or phenols.
Agaricales make up the majority of agarics, including for instance those where the lamellae are separated from the stalk. Among the Agaricacae there are also some more unusual types like puffballs, with internal spores released by splitting, and bird’s nest fungi, which form small cups with spore chambers scattered by rain.
Many types of pigments found in other groups occur here, for instance β-carotene in Chrysomphalina and atromentin derivatives in Omphalotus. Pigments related to the betalains of caryophyllid plants are found in red to yellow species of Hygrocybe and Amanita. In the former these are hygroaurins, which have yellow muscaflavin as a precursor in place of betalamic acid.
Muscaflavin also occurs in A. phalloides (death caps) and is found along with true betalains in the red to orange caps of A. muscaria (fly agarics) and the edible A. caesarea. These include a number of the same betaxanthins as plants in addition to orange muscaaurin II, derived from stizolobinic acid, and purple muscapurpurin of incompletely known structure.
Fly agarics were some of the first known hallucinogenic mushrooms. The main compound responsible is ibotenic acid, together with its derivatives muscaaurin I and muscimol; the last is the active form which triggers GABA receptors, resulting in intoxication, convulsions, dizziness, and so on. Death caps and several others have much more lethal peptide toxins.
Anthraquinones and dihydroanthrones, including a number of types found in other fungi and plants, are common pigments in Tricholoma, Cortinarius, and Dermocybe. These are responsible for red or violet colour changes with alkali. The quinones are largely acids like yellow endocrocin, or red dermorubin in the latter two genera, but others like physcion also occur.
The dihydroanthrones mostly occur in a variety of dimers, of which flavomannin dimethyl ether and derivatives are the most common. In these rotation of the central bond is blocked and so they occur as separate atropisomers. B isomers are the main pigments of yellow T. sulphureum (sulfur knights), while some Cortinarius have only A isomers; still other species have a mix of both.
The remaining classes of fungi here are all Ascomycota. These variously take the form of single cells or septate hyphae with a dikaryotic stage similar to Basidiomycota. Instead of basidia, though, sexual reproduction takes place by the production of spores on the inside of cells called asci.
Pezizomycetes usually have fruiting bodies in the form of apothecia, which have an upper layer of exposed asci when mature, and these in turn expel spores through an operculum or lid. The shape varies from cup-like to larger stalked forms with wrinkles or pits. Truffles are an exception, with fruiting bodies that remain closed underground and depend on animals to distribute the spores.
Many cup fungi are brightly coloured with carotenoid pigments. Besides common types like γ- and β-carotene these include some more unusual sorts, particularly ones with hydroxylated end groups like plectaniaxanthin. This is for instance the main colour in Sarcoscypha coccinea (scarlet cup fungi), mostly as fatty acid esters.
This is the largest group of fungi that form lichens, where they rely on photosynthesis from enclosed green or sometimes blue-green algae. Most are able to grow with little other nourishment or moisture, and have small but persistent fruiting bodies. Lecanoromycetes are usually non-gelatinous and have more or less round apothecia, though some are exceptions.
Lichens in general produce a variety of esters from β-orsellinic and orsellinic acid, called depsides and depsidones, as crystals on the hyphae. The most common here is atranorin, which absorbs ultraviolet and is found in the upper cortex; in some people it is a contact allergen or photosensitizer. This and many other cortical compounds vary with light and so screen the algae.
Other depsides and depsidones are found on interior hyphae. Some more common examples are norstictic acid, which binds to metal ions; stictic acid, another allergen; and gyrophoric acid, which inhibits plants. They also inhibit some bacteria. These are all colourless, but many of the aldehydes show as yellow or red in alkali, and orsellinic acid derivatives as red in hypochlorite.
Many lichen dyes are based on similar changes. Lichens with large amounts of aldehydes, like Lobaria with norstictic and stictic acid, give fast yellow or brown colours when boiled with wool and other fibres. Types like Umbilicaria and Ochrolechia with gyrophoric or sometimes lecanoric acid may be used for dyes similar to orchil.
Teloschistales usually have apothecia with a margin derived from the surrounding tissue, called lecanorine, and spores divided into two or sometimes four cells. These are variously brown or, in Teloschistaceae, colourless with a thick median wall, which confines the cells to the poles and often has a canal between them.
Teloschistaceae also typically have physcion, an anthraquinone also found in various other fungi and plants, usually called parietin in lichens. Here this is a light screen pigment and gives many orange or yellow colours depending on their exposure. It has also been found to protect them from snails despite their being relatively nitrogen-rich.
Lecanorales are a large and variable group. The apothecia are usually open with colourless spores, lecanorine or not, but a few have more closed types where the asci disintegrate into a dark mass. In those categories most of the larger fruticose lichens, that is to say ones with erect or pendulous stalks, belong here along with a mix of crustose, scale-like, and foliose relatives.
The main light screens here are atranorin and usnic acids, which occur as both the (+) and (–) enantiomers in different species. The latter give yellow colours to many more sun-exposed lichens and also show activity against a variety of bacteria, plants, herbivores, and so on. They have been used as antiseptics but again can be strong contact allergens.
Fumarprotocetraric acid is also relatively common here, for example in many large boreal Cladonia and Cetraria; this bitter depsidone makes them less palatable to grazers like reindeer. Some Cladonia also form rhodocladonic acid, for instance as a response to mites, a quinone which colours the apothecia pink or bright red.
Many species in the family Parmeliaceae have alternative depsidones like salazinic acid, including some used for dyes. This group also includes a few toxic lichens with vulpinic acid, which has been used for both dyes and animal poisons; this is the bright yellow cortical pigment in Letharia and Vulpicida, likely as a warning colouration.
Leotiomycetes are non-lichens united mainly by genetic trees. These usually have small apothecia where asci open through pores, found as cup- to club-shaped bodies on decomposing material, soil, or plants. The parasitic powdery mildews, though, have cleistothecia with radiating appendages, which typically release spores when they are burst by moisture.
This is another group where β-carotene is a common pigment. There are also a few with quinone dimers, notably xylindein in Chlorociboria, which gives the cups a distinctive bluish-green colour as well as staining the wood where they grow. The black fruiting bodies of Bulgaria inquinans contain some simpler purple to deep red types like bulgarhodin.
Arthoniomycetes mostly form lichens with symbiotic green algae. They typically have bitunicate asci, with two differentiated walls, where the inner one expands and bursts through the outer one to release the spores. These occur in round to elongate apothecia, sometimes in the form of more peculiar slit-like or branching hysterothecia.
Many kinds have depsides, depsidones, or other compounds also found in Lecanoromycetes, most commonly lecanoric acid. Some also have its ester erythrin, identified as the (+) enantiomer in at least Roccella montagnei, which were a major source of orchil. Several species are also used to make litmus; both are red to purple dyes formed by reaction with oxygen and ammonia.