Mushrooms that are individual teeth that hang down have their own category, teeth, and mushrooms with longer individual spines rising upwards are in the club and earth tongue categories. This category is for flat or wrinkled surfaces or surfaces with small teeth <3mm embedded in a flat surface. I have not yet noted as many distinctive microscopic features as I do on other pages (such as amyloid or ornamented spores). Thorough coverage of the crusts is beyond the scope of this key. What follows is an overview of some of the more distinctive species.
Exceptions: Crusts that belong elsewhere:
Kretzschmaria deusta - Ascomycota "flask" with sometimes difficult to detect pimples. Dual tone white and grey, aging to black. Hardwoods.
Apiosporina morbosa - black knot of cherry - a black crust surrounding branches of cherry and plum trees. In a different class than any other mushroom on these pages - the Dothideomycetes.
Trichoderma sp. - actually a flask, but often a non-pimpled fuzzy mold, that appears to turn blue-green when the white surface is scratched. On wood.
Claviceps purpurea - also a flask, parasitizes rye and other grasses, starting as a dark purplish crusty sclerotia.
Lichens (covering perhaps 6% of the earth's land surface!) resemble crusts, but are unrelated Ascos. A lichen is the symbiosis of a fungus and green algae or cyanobacteria. Don't be fooled by a lichen that resembles a crust fungus (or even a cup or coral fungus). They will often have some shade of green. Lichens are not covered by these keys.
Most crusts are saprophytic, although some could potentially be parasitic, and a very few interesting species may grow on the ground instead of wood and actually be mycorrhizal, even when they are found on wood! (Such as Piloderma and Byssocorticium). As you will see, almost every branch of the mushroom family tree has a crust in it. No matter how complicated a mushroom has become, it probably has a primitive relative that started out as a simple crust.
Key to Crusts:
Cap - wrinkled surface: First we have the species that are not entirely resupinate, but also have a cap bending away from the wood, called effuso-reflexed or semi-resupinate. Underneath the cap (and the entire surface that is on the wood) is not smooth, but wrinkled, veined or covered in tiny teeth. The first three are in the Polyporales and may represent intermediate evolutionary steps on the way to evolving pores. Ditto for Pseudomerulius which is related to boletes (Boletales). Plicatura and Plicaturopsis are distant relatives of gilled mushrooms (Agaricales), and may represent intermediate evolutionary steps on the way to evolving gills.
Byssomerulius (Meruliopsis) corium - white on hardwood sticks, edges hanging off. Wrinkled underneath, faintly zoned above. 5-10cm. Other species are resupinate.
Steccherinum ochraceum - white to orange-brown cap and teeth, toothed underside. Caps stick out ~1cm. Other species are resupinate.
Plicatura nivea - white to beige, wrinkled or blunt ridges less defined than Steccherinum teeth. Hardwoods. Caps extend 1-3cm.
Pseudomerulius - bright orange, also resupinate with other lookalike species, see below.
Cap - Smooth: a cap peels away from the flat surface, but the underside and part that lies flat on the wood is smooth or almost completely so.
Stereum - the most common genus in this category by far, recognized by a bright orange or dull orange-tan underside and flat surface, as well as a somewhat hairy, orange, concentrically zoned cap. They grow most often on hardwoods. Some are called false turkey tails because of their resemblance to Trametes (which are pored underneath). These are related to the Russulas (Russulales).
S. sanguinolentum - dull, barely orange, resupinate on conifers, stains red when scratched. Much like Phanerochaete.
Pseudochaete (Hymenochaetopsis) tabacina - orange-brown zoned cap like Stereum with possible white margin, tobacco, coffee brown underneath. (Hymenochaetales with setae like Phellinus) Hardwoods, projecting <2cm.
Hymenochaete rubiginosa - less resupinate, oak, red- to grey-brown. Others are resupinate. These turn black in KOH.
Veluticeps fimbriata - brown cap, grey under on barkless conifers, projecting <4cm.
V. abietina - caps angled down sharply. (Gloeophyllales)
Amylostereum - conifers, similar (Russulales)
Chondrostereum purpureum - violet underneath, fading in age, on hardwood, projecting <2cm. (Agaricales) Related to the gilled mushroom Marasmius!
Resupinates: These mushroom lie entirely flat on the wood, with no cap sticking out.
Resupinate - Staining: When you touch or scratch these crusts, or in age, they change colour.
Phanerochaete sanguinea - on conifers, turns red without being touched, but irregularly so it looks like its a staining reaction.
Even when P. sanguinea is not fruiting, the presence of the mycelium stains wood red! Much like Chlorociboria stains wood blue. (Polyporales)
Stereum sanguinolentum - on conifers, only turns red where scratched, the wood itself is not red. (Often with a cap too).
Peniophora polygonia - pinkish white crust, staining red-brown when rubbed, not blood red. (Russulales)
Eichleriella deglubens - a similar pink, slightly warty more spread out crust on hardwoods that turns wine-red when injured. (Auriculariales)
Resupinate - Wrinkled: folds, veins, ridges, or perhaps tall irregular projections, but not individual spines or teeth.
Phlebia etc. - Phlebia is a relative of the Polyporales, and has a waxy or jelly-like consistency. The last six unrelated species may also be soft, but are not quite as jelly-like or waxy as Phlebia.
Peniophora rufa - little red tree brains, but not gelatinous like some similar mushrooms. Hardwoods. (Russulales)
Cytidia salicina - red, bumpy surface, less isolated than Peniophora rufa. Hardwoods. (Corticiales)
Resupinate - Teeth: a collection of individual spines sticking up taller than they are wide. Small bumps are far too common to be able to cover here. Mucronella is usually considered to be a cluster of individual clubs and is found on that page, but might be seen as a crust and looked for on this page.
Kavinia alboviridis - long, sparse spines, greenish tinged on a white mycelial mat. Other species are white. (Gomphales)
|Cristinia eichleri (gallica) - bright
yellow with blunt, irregular
Steccherinum ochraceum - see above in effuso-reflexed, sometimes a resupinate.
Steccherinum fimbriatum - pinkish lilac, fringed, many small bumpy teeth. (Polyporales)
Dentipellis fragilis - white with long teeth (~1cm) (Russulales)
|Other genera with pale tooth crusts are found in many different orders: Polyporales (Dacryobolus), Hymenochaetales (Asterodon, Hyphodontia), Cantharellales (Sistotrema), Auriculariales (Protohydnum) and Trechisporales (Trechispora). It is not practical to try and separate them macroscopically.|
Resupinate - smooth-ish, waxy-gelatinous: like the jellies, soft and gelatinous or perhaps waxy, but unlike the jellies, lying flat as a crust on the wood. Many of the species described earlier on this page are soft and waxy, but they also have some other distinguishing features.
|They are found in many different orders: Auriculariales (Basidiodendron, Eichleriella, Exidiopsis, Stypella), Sebacinales (Sebacina), Cantharellales (Ceratobasidium, Sistotrema, Tulasnella), Dacrymycetes-Dacrymycetales (Cerinomyces), Polyporales (Hyphoderma, Phlebia, Phlebiopsis, Xenasma), Agaricales (Radulomyces), Hymenochaetales (Peniophorella, Repetobasidium, Resinicium, Tubulicrinis) Russulales (Gloeothele, Peniophora). They are relatively rarely collected and difficult to tell apart.|
Resupinate - smooth-ish, colourful: May be smooth or bumpy, but the bumps are not taller than they are wide. They are colourful or dark instead of off-white. There are dozens if not hundreds of pale yellow, orange and grey species, so you have to be pretty bright or dark to make the cut here. This is only a small sampling, there are many others occasionally found.
Phlebia subochracea - waxy, not as wrinkled as other Phlebias, which you should also consider. Hardwoods.
Xenasmatella vaga (Phlebiella sulphurea) is very similar but cottony. (all Polyporales)
Tomentellopsis echinospora - yellow and cobwebby.
Tomentella and Pseudotomentella spp. are often brown cobwebby. Amaurodon spp may be greenish. (all Thelephorales)
Piloderma fallax - yellow threads. The rhizomorphs are yellow and thick enough to see! (Atheliales) This order has many wispy-looking spp, mostly white.
Byssocorticium spp in this order may be blue-green.
Cytidia salicina - red, bumpy surface, less isolated than Peniophora rufa. Hardwoods.
Aleurodiscus grantii - orange fringed discs, on true fir, resemble cup fungi. (Russulales). <5mm
Hymenochaete cinnamomea - bright, rusty. (Hymenochaetales - has setae like related Phellinus and Inonotus spp. and all turn black in KOH). Hardwoods.
Peniophora cinerea - hardwoods. Grey. (Russulales)
sanguinea, above, will be colourful if the red staining has already
Tulasnella spp. (Cantharellales), Xenasma (Polyporales), Oliveonia (Auriculariales) and Helicobasidium (Pucciniomycetes - a "rust") may be lilac to purple mixed with grey like Peniophora, but are soft and waxy.
Resupinate - smooth-ish, pale: Smooth or bumpy, with bumps that are not taller than they are wide. Pale crusts are probably the most difficult of all mushrooms in the world to identify. There are hundreds of them, and they pretty much all look the same. Some are waxy, some are fringed at the margin or wispy throughout the crust, but as it says in Fungi of Switzerland volume 2/#239, "Identification of the species described here on the basis of purely macroscopic features is scarcely imaginable". You're going to need a microscope and a lot of practice with it to be able to identify mushrooms in this group. You might choose to do what many people do - decide that these are "not really mushrooms" and outside your scope of interest.
It is remarkable just how many different orders contain independently evolved similar looking crusts. One can certainly think of a crust as a basal form for many different kinds of mushrooms - Agaricales, Russulales, Boletales, Polyporales, Hymenochaetales, Gloeophyllales, Corticiales, Thelephorales, Cantharellales, Auriculariales, Gomphales, Sebacinales, Atheliales, Trechisporales - more than any other similar looking group.
For now, these are mostly beyond the scope of these pages.
Aleurodiscus penicillatus is sometimes recognizable as small pale pinkish white patches a few mm or so each on small twigs. Turns black in iodine. (Russulales)
There is nothing local, but Fungi Europaei Volume 12 Corticiaceae s.l. by Bernicchia and Gorgón has ~425 colour photographs and ~450 microscopic feature drawings of crusts from Europe, many of which appear here, and it is considered one of the bibles of crusts. Remarkably, it is in English. The other important general work is the already mentioned Volume 2 of Fungi of Switzerland, available as an option entirely in English.