Abhymenial surface: The sterile upper surface of an effused-reflexed or pileate crust (see basidioma).
Aphyllophorales: Obsolete taxonomic category for homobasidiomycetes without gills ("a-" prefix meaning "not, without"; "phyllo" meaning "a leaf, leaf-like", i.e. gills), which included crust fungi, polypores, coral mushrooms, and others, but excluded puffballs, which were given there own (also now-obsolete) 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.
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.
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.
The following terminology presents a standardized set of terms to discuss basidiospore shape as a function of the basidiospore quotient.
Other shapes that are not defined by basidiospore quotient, or might apply to any shape designated above, are as follows:
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 traits listed below. I try to measure 10 basidia, from the basal septum to the apex (excluding the sterigmata), with the width taken at the widest part.
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 pedestals 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.
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 that are also heterobasidiomycetes belong in the Agaricomycetes, like Auriculariales, Sebacinales, and some families in Cantharellales, which means heterobasidiomycetes is a paraphyletic grouping. There are lots of good crust-like fungi in Auriculariales, Cantharellales, and Sebacinales, so I don't exclude heterobasidiomycetes from this website. Heterobasidia can be longitudinally (vertically) septate or transversly (horizontally) septate. If a basidium is longitidunally septate with four sterigmata, it is deemed cruciate (because the septa create the appearance of a plus sign when viewed from above).
Homobasidiomycete: Basidiomycete whose basidia are not septate (contrast with heterobasidiomycete). This grouping corresponds to most fungi in Agaricomycetes and, subsequently, most crusts.
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.
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.
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 main types of hyphae (generative and binding or generative and skeletal). Trimitic contain all three. Sometimes the presence of modified tramal hyphae, like dichohyphae in Vararia investiens, earns a species the dimitic designation.
Hyphidium (plural: hyphidia): Hyphidia are modified terminal hyphae in the hymenium (or, if in the trama, the suffix -hyphae instead of -hyphidia is applied).
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.
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.
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.
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 and other fungal cells. 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. Septa can also sometimes be found in cystidia and basidia (see heterobasidiomycetes vs. homobasidiomycetes).
Sterigma (plural: sterigmata): The prong-like tips of basidia upon which basidiospores 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)
Wood rot: Wood is composed of the polymers cellulose, hemicellulose, and lignin. Crusts that eat wood can be divided into two categories: white rot fungi and brown rot fungi. White rot fungi degrade cellulose, hemicellulose, and lignin, resulting in bleached, stringy wood. Brown rot fungi ignore the lignin, focusing instead on the cellulose and hemicellulose. The resulting decayed wood is brown and often cubical and crumbly.
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.