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If you have a leathery, downward facing cup on wood, check Stereum
- especially if the outer surface of the cup is furry or hairy.
If you don’t have a Stereum, read on.
The fruitbody of a fungus in this sub-group may be stemless or with a stem. In the first case the fruitbody is either fairly flat and disk-like or with a slight curvature and saucer-like or with a pronounced curvature and then cup-like (perhaps even with the rim folding inward). In the second the fruitbody consists of a disk/saucer/cup atop a stem. The disk-like to cup-like component ranges from a millimetre to 10 or so centimetres in diameter. When viewed from above the individual fruitbodies in most species are circular in outline but if they grow densely packed mutual pressure often distorts the circular outline. Even single fruitbodies that are several centimetres in diameter may become distorted to some degree.
In the majority of the species in this group the disk or cup is an apothecium. In an apothecium the spores are produced within microscopic pods, mostly elongated, called asci. The asci (along with sterile spacing tissue) are lined up palisade-like and that palisade constitutes the apothecium’s upper surface (i.e. the one that faces away from the substrate). A fungus that produces spores in asci is called an ascomycete. Apothecial ascomycetes are also known as discomycetes and, especially in field guides aimed at the amateur, are referred to colloquially as cup fungi.
Another type of ascomycete fruitbody is a perithecium. This is a roughly spherical chamber within which you find asci and sterile tissue. Perithecia are usually small, from under a millimetre to about 2 mm in diameter. Sometimes a number of perithecia growing as a community, embedded within communal tissue and all that the naked eye sees of the embedded perithecia are their dot-like or pimple-like apices (and the species of Poronia show this in a disk-like growth form).
There are a few non-ascomycete genera with disk-like to cup-like fruiting bodies. From just the outward form alone you cannot tell whether you have an ascomycete or not.
In fungal guides, the expression ‘cup fungus’ is confined to cup-like ascomycetes (and that usage is an accident of history). So, a fungus that produces a cup-like fruitbody need not belong to the cup fungi.
In the following hints you see examples of useful identification features and a few of the more commonly seen genera in which at least some species (not necessarily all) show those features.
White disk with black dots: Poronia.
Blue to green: Chlorociboria.
Orange to red: Aleuria, Anthracobia, Cheilymenia, Pyronema, Scutellinia.
Orange, margin with long, brown, eyelash-like hairs: Scutellinia.
More than 2 centimetres in diameter: Aleuria, Discina, Peziza, Plectania.
On burnt soil: Anthracobia, Pyronema.
On herbivore dung: Ascobolus, Cheilymenia, Poronia.
Cups growing so densely packed as to give the impression of a flat polypore: Merismodes.
Waxy upper surface, densely furry margins and lower surface: Eichleriella.
Greyish cup, to 3 cm across, stem length equal to (or longer than) cup diameter: Helvella.
Shallow cups merging to create a composite fruitbody of irregular shape: Eichleriella.