Glossary of Mycological Terms

Abhymenial surface: The sterile upper surface of an effused-reflexed or pileate crust (see basidioma).


Aphyllophorales: Obsolete taxonomic category for homobasidiomycetes without gills, which included crust fungi, polypores, coral mushrooms, and others, but excluded puffballs, which were given there own category called Gasteromycetales.


Anamorph: Asexual fruiting body of a fungus (contrast with teleomorph, the sexual fruiting body). In the past, anamorphs and teleomorphs of the same species were each given their own Latin binomial, either because mycologists didn't know they belonged to the same species or because it was convenient to refer to them separately. The "one fungus, one name" movement in mycology has done away with this convention although old names still float around (for example, Haplotrichum in reference to the anamorphs of Botryobasidium species; Rossman et al. 2016).


Apiculus: Also called the hilar appendix, an apiculus is a short protrusion at the end of a basidiospore where the basidiospore attaches to the sterigma. Apiculate is a descriptor for a basidiospore with a well defined apiculus.


Basidioma/e (plural: basidiomata): Also called basidiocarp, fruiting body, or mushroom, the basidioma is the macroscopic sexually reproductive structure of basidiomycete fungi. Basidiomata are highly variable in size, shape, texture, and color. While the bulk of any filamentous fungus exists as mycelium in the substrate, fungal identification and taxonomy relies almost exclusively on the (typically) ephemeral basidiomata. Basidiocarps are often annual (persisting for less than one year) but some are perennial (persisting for multiple years). Resupinate basidiocarps consist of a hymenium (outermost fertile layer with the basidia and sterile structures such as cystidia, also called the spore-bearing surface), subhymenium (layer of hyphae below the basidia, sometimes compact and strongly branched, may be lacking in very thin crusts), trama (layer of tissue supporting the subhymenium and hymenium, but only used for hymenophores that are poroid, hydnoid, etc. but not smooth or even ones), and subiculum (hyphae next to the substrate, mostly growing parallel to the substrate and typically wider and thicker than the subhymenial hyphae). If the basidiome is anything other than effused, it will have an abhymenial surface (surface of the cap), which can be smooth or hairy. For descriptors of abhymenial surface hairiness, see hymenophore consistency. In addition to their growth form, basidiomata are further described by their hymenophore and margin.

Growth form

  • Effused — a completely resupinate basidioma and therefore one with no sterile surfaces except for the margin; entirely adherent to the substrate
  • Orbicular — circular
  • Effused-reflexed — an effused basidioma whose margin grows away from the substrate to form a small cap, or pileus (reflexed margin)
  • Cupulate or discoid — an orbicular, effused-reflexed crust that takes on the appearance of a cup fungus
  • Dimidiate — fan-shaped pileus
  • Stipitate — basidioma with a stem, or stipe
  • Decorticant — basidioma that develops under bark and then pulls up and away when mature

Basidiospore: The sexual, propagative spore of basidiomycete fungi. Basidiospores are produced via meiosis and are born on the sterigmata of basidia, usually with four basidiospores produced per basidium, but varying between one and eight. The number of basidiospores per basidium as well as their size, shape, ornamentation, wall thickness (thin-walled or thick-walled), color (hyaline or colored), and any chemical reactions are all important for species identification. Wall thickness is very subjective, but in general if you can make out a distinct wall around the spore, it would be considered thick-walled. Hyaline spores are see-through or transparent.

Size

One should always measure mature, liberated basidiospores rather than basidiospores that are attached to sterigmata, which might not be fully developed and therefore be smaller than what's reported in the literature. This can be ensured by measuring basidiospores that have been naturally released from basidia in the formation of a spore print. Try to measure basidiospores that are "flat" (not askew, which throws off length) and make sure to exclude the apiculus and ornamentations in your measurements. I try to measure 30 basidiospores per specimen. This can be done quickly from a spore print. The basidiospore quotient is the length to width ratio, which is tabulated for each spore. In the species profiles, I report sizes as the mean ± one standard deviation surrounded by the minimum and maximum measurements in parantheses.

Shape

The following terminology presents a standardized set of terms to discuss basidiospore shape as a function of the basidiospore quotient.

  • Globose — Q = 1–1.05
  • Subglobose — Q = 1.05–1.15
  • Broadly ellipsoid — Q = 1.15–1.3
  • Ellipsoid — Q = 1.3–1.6
  • Cylindrical — Q = 1.6–2
  • Narrowly cylindrical — Q = 2–3
  • Allantoid — Q = 3–4
  • Fusiform — Q = 4–6

Other shapes that are not defined by basidiospore quotient, or might apply to any shape designated above, are as follows:

  • Curved or sausage-shaped — bent; allantoid is sometimes used to refer to sausage-shaped spores regardless of their quotient
  • Amygdaliform — almond-shaped
  • Fusoid — tapered and point on both ends
  • Lacrymoid — shaped like a tear drop, specifically one with a somewhat curved tip
  • Ovate — oval-shaped
  • Pyriform — pear-shaped
  • Navicular — boat-shaped, like a row boat in profile
  • Reniform — kidney-shaped
  • Tetrahedral — shaped like a triangular pyramid

Ornamentation

  • Smooth — no ornamentations
  • Asperulate — roughened by many small points or warts
  • Echinulate — roughened with small spines or prickles
  • Tuberculate — roughened with small rounded projections or protuberances
  • Warted — roughened by relatively large protuberances
  • Striate — coated with linear ridges

Basidium (plural: basidia): The sexually reproductive cell characteristic of fungi in the phylum Basidiomycota (and therefore, all crust fungi) where karyogamy of the two haploid nuclei and meiosis occur leading to the production of basidiospores. Basidia vary greatly in their form, but they all have sterigmata (horn-like projections on the apical part of a basidium, usually with four sterigmata per basidium but varying from one to eight) upon which basidiospores are formed like inflating balloons. In addition to number of sterigmata per basidium, the presence or absence of a basal clamp is important for identification as well as the following traits.

Internal septation

  • Holobasidium — basidium without septa, most common type and defining feature of homobasidiomycetes
  • Phragmobasidium — basdium divided by horizontal or cruciate septa, infrequent in crusts, defining feature of heterobasidiomycetes

Type

  • Terminal or apical — formed at the end of a generative hypha
  • Pleural — laterally formed from a generative hypha and with an enlarged, sometimes bifurcate base
  • Repetitive — basidum that originates from older basidia via internal repetition, with the older basidia remaining as a sheeth around the base of the new basidium

Shape

  • Cylindrical — relatively constant width across the entire basidium
  • Clavate — shaped like a club
  • Constricted — basidium with pinched sections
  • Urniform — shaped like an urn
  • Utriform — shaped like a leather bottle (one with a central constriction)
  • Stalked — basidium subtended by an elongated stalk
  • Subglobose — short, squat, nearly round basidium

Bladder structure: A very strange type of sterile structure in the hymenium. Echinocysts consist of a rounded bladder covered with sparse, blunt projections. Stephanocysts are crowned pedestal that suspend a sphere of homogenous fluid.


Corticioid fungus: Also called crust or crust fungus, a basidiomycete whose basidioma is generally resupinate (see the introduction).


Cystidium (plural: cystidia): A sterile cell, embedded or projecting from the hymenium, differently shaped from the basidia. Cystidia are very useful for identification, but their adaptive function is largely a mystery.

Location

  • Cheilocystidia — occuring on the edges of the gills or pores, sometimes conferring a distinct color
  • Pleurocystidia — occurring on the faces of the gills or inside the pores
  • Dermatocystidia or pileocystidia — occurring on the surface of the cap
  • Circumcystidia — occurring on the margin of the cap
  • Caulocystidia - occurring on the stipe

Origin

  • Hymenial cystidia — arising in the hymenium or subhymenium
  • Pseudocystidia — arising from the trama or subiculum
  • Skeletocystidia — originating from the terminal, enlarged part of skeletal hyphae

Form

  • Hyphocystidia — very simple hypha-like cystidia originating in the subhymenium and projecting beyond the hymenium, akin to paraphyses
  • Leptocystidia — most common type of hymenial cystidia, thin to moderately thick-walled, cylindrical to fusoid to conical, sometimes encrusted
  • Gloeocystidia — hymenial cystidia or pseudocystidia, tubular or vesicular, often sinuous or constricted along their length, with thin walls and abundant hyaline or yellowish oily content in the cytoplasm
  • Moniliform cystidia or torulose cystidia — regularly constricted leptocystidia or gloeocystidia, like a string of beads
  • Capitate cystidia — cystidia with a distinct apical swelling; subcapitate is used to refer to only slightly apically swollen cystidia
  • Septocystidia — cystidia with regular septa, often with clamp connetions, typically cylindrical, thin- or thick-walled
  • Lyocystidia — distinct cystidia characteristic of some genera (e.g., Dacryobolus, Litschauerella, Odonticium, Tubulicium, Tubulicrinis) in Hydnodontaceae and Tubulicrinaceae consisting of very thick, refractive walls, a small capillary cytoplasm, which widens abruptly at the apex forming a tip, and two or more rooting hyphae; the walls dissolve in KOH, which is an example of why crusts should always be observed in tap water in addition to other mounting media
  • Lamprocystidia or metuloids — cystidia consisting of a basal part with thin walls and a large lumen, and an apical part that is thick-walled and conical with a thin, capillary lumen and extensive encrustations; not always distinguishable from thick-walled, encrusted leptocystidia
  • Subulate cystidia or subulicystidia— in its most basic form, cystidia that taper to a point like an awl, but also specialized cystidia in the genus Subulicystidium that consist of a hypha protruding from a needle-tipped, thick-walled crystalline sheath oranmented with regular, rectangular encrustations
  • Lageniform cystidia — cystidia with a broad basal part and needle-like, encrusted apical part, like a bottle brush
  • Astrocystidia or asterocystidia — cystidia with a star- or pompom-like cluster of crystals at the tip
  • Halocystidia — cystidia with a capitate apex surrounded by a large resinous droplet
  • Acanthocystidia — cystidia that are described as antler-like, covered with apical protuberances
  • Schizopapillate cystidia — cystidia with an apical constriction, kind of like that weird pokey end of a semi-deflated balloon
  • Mucronate cystidia — similar to schizopapillate, but in reference to a more acute protuberance at the apex

Guttulate: Containing one or more oil droplets (guttules) in the cytoplasm.


Heterobasidiomycete: Basidiomycete whose basidia are septate (contrast with homobasidiomycete). Heterobasidiomycetes were often excluded in the treatment of crusts because they were thought of as an evolutionarily and taxonomically distinct category. And they are, in a way, as fungi in the subphyla Pucciniomycotina and Ustilaginomycotina, as well as the classes Tremellomycetes and Dacrymycetes in Agaricomycotina, are all heterobasidiomycetes (basically all groups except for the class Agaricomycetes, which was considered synonymous with homobasidiomycetes). However, molecular phylogenetics revealed that some groups in the Agaricomycetes are also heterobasidiomycetes, like Auriculariales, Sebacinales, and some families in Cantharellales, which means heterobasidiomycetes is a paraphyletic grouping. There are lots of good crusts in Tremellomycetes, Auriculariales, Cantharellales, and Sebacinales, so I don't exclude these fungi from this website.


Homobasidiomycete: Basidiomycete whose basidia are not septate (contrast with heterobasidiomycete). This grouping corresponds to most (but not all) fungi in Agaricomycetes.


Hyaline: Transparent and colorless.


Hymenophore: The tissues that support the hymenium. Technically, this refers to the subiculum, trama, and subhymenium. The hymenophore is described by its configuration and consistency.

Configuration

  • Punctate — with small depressions
  • Poroid — with more or less regular, defined pores
  • Smooth or even — flat
  • Phlebioid — with irregular but not anastomosed folds; phlebioid is also sometimes used as a descriptor of consistency in reference to the typical Phlebia texture, which is dense and hard, ceraceous when fresh and crustaceous when dry
  • Merulioid — with irregular and anastomosed folds, sometimes poroid with irregular and fertile edges
  • Reticulate — net-like folds and ridges
  • Granulose — with minute granules
  • Grandinoid — with small, rounded grains
  • Papillate or colliculose — with small, rounded projections
  • Tuberculate — with more prominent, round, wart-like projections
  • Odontioid — with cylindrical to conical projections
  • Hydnoid — with prominent spine-like projections
  • Irpicoid or dentate — with irregular, tooth-like projections
  • Raduloid — with flat, wide, rounded projections

Consistency

  • Pruinose — finely powdery or frosted, like the surface of grape
  • Farinaceous — mealy, minutely granulose, more or less discontinous
  • Chalky — with a chalky appearance or texture
  • Arachnoid — discontinous fruiting body, very loosely interwoven hyphae like a spider web
  • Fibrillose — loosely interwoven hyphae forming a net
  • Byssoid — floccose, or cotton-like
  • Athelioid or pellicular — thin and easily detachable, like old, peeling skin
  • Membranaceous — thin and attached, with a skin-like consistency
  • Ceraceous — waxy
  • Coriaceous — tough, like leather
  • Crustaceous — hard, like a crustacean shell
  • Scuprose — rough due to small, pointed bundles of hyphae
  • Velvety — with short, dense and velvety hyphae
  • Pilose — with long, soft, dense filaments
  • Hispidus — with erect and rigid hairs
  • Tomentosus — with dense, wooly hairs

Hypha (plural: hyphae): The fundamental cellular unit of all filamentous fungi (and therefore all crusts). Hyphae are thread-like or tube-like cells that weave together to form the mycelium (the web-like "body" of a fungus that grows through the substrate feeding on organic matter) as well as the basidioma (the macroscopic reproductive structure, or mushroom). When describing a basidioma, hyphae should be observed and measured in the different layers. I always measure subicular hyphae and subhemnial hyphae separately, with 10 width measurements per section, expressed as the mean ± one standard deviation surrounded by the minimum and maximum values in parantheses. Crystal or resinous encrustations are also common on hyphae and can be diagnostic.

Types

  • Generative hyphae — the basic and universal type of hyphae of all crusts; generative hyphae are always septate, but otherwise vary between species and sometimes even within a single fruiting body in width, wall thickness (think- or thick-walled), type of septa (simple or clamped), cytoplasmic content, branching, and color
  • Binding hyphae — one of two types of "vegetative" hyphae that develop from generative hyphae; highly branched, tapered, of limited growth and with thick walls; rare in crusts
  • Skeletal hyphae — one of two types of "vegetative" hyphae that develop from generative hyphae; long, straight, unbranched hyphae without septa; also rare in crusts, but sometimes present in the subiculum

Hyphal system: A reference to the number of distinct types of hyphae present in a fruiting body. Monomitic fungi only contain generative hyphae, which is by far the most common type of hyphal system in crusts. Dimitic fungi contain two of the three types of hyphae (generative and binding or generative and skeletal). Trimitic contain all three.


Hyphidium (plural: hyphidia): Hyphidia are modified terminal hyphae in the hymenium (or, if in the trama, the suffix -hyphae instead of -hyphidia is applied).

  • Dichohyphidia — dichotomously branched hyphidia
  • Dendrohyphidia — irregularly and strongly branched hyphidia, like tree branches
  • Asterohyphidia — hyphidia with stellate branching
  • Acanthohyphidia — hyphidia with a bottle-brush appearance

Margin: The edge of a basidioma. It can be sterile or fertile, abrupt (without a thin, sterile margin), distinct, smooth, arachnoid (loose like a spider web), byssoid (cottony), fimbriate (with radiating hyphae), or rhizomorphic (with hyphal strands).


Mounting medium: A liquid placed on a glass slide into which a piece of fungal tissue is deposited and then covered with a cover slip to be observed under a compound microscope. Different mounting media, with or without additional stains, are useful for different aspects of microscopy and for observing different structures. Some mounting media also serve as chemical reagents in whose presence color changes may occur, which are very useful for identification. For a useful overview of chemical reagents and the preparation of other chemicals used in fungal microscopy, see this primer by the British Mycological Society.

Tap water is useful for seeing fungal structures "as is". Some encrustations, cystidia, or bladder structures collapse or dissolve if placed in other media. However, crusts are generally hydrophobic so the tissue may be covered with bubbles and difficult to observe in tap water, especially because hyaline tissue is difficult to see without a stain. At the other end of the spectrum, some fungal tissue can be so densely encrusted that hydrochloric acid needs to be used to clear the crystals (I have not done this before and urge caution if you do).

Potassium hydroxide (KOH) (or ammonium hydroxide) stained with phloxine (also called phloxine B) is the standard mounting medium. KOH is very good at dispersing the tissue, unlike tap water, because hyphae are typically hydrophobic. A drop of KOH is placed on the glass slide. Then, the dropper with phloxine is every so slightly tapped against it to release some stain. I first expel all phloxine from the dropper before tapping it so I'm just transferring a little bit of residual stain left on the tip of dropper. Phloxine is very powerful and can easily overwhelm the specimen. The tissue should be bright red from absorbing the stain while the background stays pink. If the entire field of view is bright red, too much phloxine was used. In this case, and in general, you can add a drop of KOH to one end of the coverslip and suck out the stain with the edge of a paper towel from the other to "wash" out the stain, but spores will be carried away so I generally avoid this technique. Phloxine will stain anything it touches — your skin, clothes, table, whatever — so be careful. Of course, KOH can be used without adding phloxine. Finally, KOH can be placed directly on the fruiting body to observe color changes. KOH has a shelf life of about a year, until precipitates form; the shelf life of phloxine is not specified and is therefore supposedely indefinite.

  • Xanthochroic — darkening on alkalization (especially common in the Hymenochaetales); this term is confusing because it is also refers to people with "light hair and pale complexions"

3-5% KOH (3-5 g KOH in 97-95 mL distilled water, or diluted from stock solution), phloxine (1.5 g phloxine in 98.5 mL distilled water)

Lactophenol cotton blue is a general stain and is also used to observe whether structures are acyanophilous or cyanophilous. Cyanophily may be difficult to observe because the cytoplasm also absorbs the stain. The tissue needs to sit in cotton blue for half an hour so that the lactic acid can properly swell the cytoplasm. The slide can be warmed with a spirit lamp, if available, to speed up the process. Some mycologists make all their microscopic measurements in this medium. Cotton blue keeps for several years.

  • Acyanophilous — no distinct darkening of cell walls in cotton blue
  • Cyanophilous — the walls of basidiospores, cystidia, basidia, or hyphae turn dark(er) blue in the presence of cotton blue

5 mL of 1% cotton blue (1 g cotton blue in 99 mL distilled water), 10 g lactic acid, 10 g phenol, 15 mL glycerine, 5 mL water

Melzer's reagent is very important for the identification of crust fungi but is difficult to acquire. That's because chloral hydrate is a schedule IV controlled substance. The reaction of fungal tissue in Melzer's reagent is often one of the first questions asked in keys. I hope the synoptic key will allow for species identification without relying on Melzer's. However, basidiospore ornamentation is sometimes not visible without Melzer's and identification is certainly facilitated by its use. This reagent apparenty doesnt' go bad - mycologists use decades-old solutions.

  • Inamyloid — no color change in the presence of Melzer's reagent
  • Amyloid — a bluish or greyish reaction in Melzer's reagent
  • Dextrinoid — a reddish brown reaction in Melzer's reagent

20 mL distilled water, 1.5 g potassium iodide, 0.5 g iodine, 20 g chloral hdyrate

Sulphovanilline is used to color the contents of gloeocystidia. If positive, it gives a black color. I have never used this reagent because it seems like a pain given its short shelf life (days) and the dangers of using strong acid. The stained tissue itself only lasts for about 10 minutes due to the destruction of the acid.

5 mg pure vanillin, 6 mL 80% sulphuric acid


Resupinate: A fungus that is growing attached or adnate to a substrate, typically on the underside of a substrate.


Septum (plural: septa): The cross wall that divides and defines individual hyphae. Simple septa are normal cross walls of the same thickness as the hyphal cell wall. Clamped septa are ones that are bridged by a little loop or buckle. Clamps can be universal (occurring at all septa), scattered (present at only some septa, either throughout the fruiting body or maybe only on the subicular or subhymenial hyphae), or absent. They can occur singularly, as a pair (double), or multiple whorled around the septum (verticillate). Basal clamps are clamps at the base of basidia. Whether a fungus has simple septa or clamped septa is very important for identification.


Sterigma (plural: sterigmata): The prong-like tips of basidia upon which basidospores are produced like inflating balloons.


Sterile structure: Non-reproductive structures in the hymenium such as cystidia, hyphidia, and bladder structures.


Teleomorph: Sexual fruiting body of a fungus (contrast with anamorph, the asexual fruiting body)


References

Bernicchia, A. & S.P. Gorjón. (2010). Fungi Europaei, Volume 12: Corticiaceae s.l. Massimo Candusso, Italia.

Hjortstam, K., Larsson, K.-H. , & Ryvarden, L. (1988). The Corticiaceae of North Europe, Volume 1. Fungiflora, Oslo, Norway.

Jülich, W. & Stalpers, J. A. (1980). The Resupinate Non-poroid Aphyllophorales of the Temperate Northern Hemisphere. North-Holland Publishing Company, Amsterdam, Oxford, New York.

Kuo, M. & Methven, A.S. (2014). Mushrooms of the Midwest. University of Illinois Press.

Rossman, A. Y., Cavan Allen, W., & Castlebury, L. A. (2016). New combinations of plant-associated fungi resulting from the change to one name for fungi. IMA Fungus, 7(1), 1–7. DOI