#179: The Genus Crepidotus

Crepidotus species are small, brown-spored agarics that grow on wood and either lack a stipe or have a diminutive stipe. These features are usually enough to separate Crepidotus species from mushrooms with a similar habitat and morphology; most other morphologically similar mushrooms produce pale spores. Although commonly encountered, Crepidotus is not useful for anything and the mushrooms go ignored by most seasoned foragers.^1,2

Description

Mushrooms in the genus Crepidotus (sometimes ‘crep’ or ‘creps’ for short) are some of the most disappointing mushrooms around. They are not useful for anything, they often fruit in abundance when you can’t find anything else, and they are difficult to identify down to species. If you’re lucky (and happen to be in eastern North America), you may come across a bright red C. cinnabarinus, but that’s about as interesting as these species get. Most of the mushrooms are small and drab.¹

In general, species of Crepidotus are small, have pale flesh, produce brown spores, and lack a stipe. The mushrooms grow only on wood and produce a thin pileus that grows up to 5cm across and is usually whitish or brownish in color. Underneath, the similarly colored gills radiate out from a central point of attachment. The gills often become more brownish as the spores mature. Spores dropped by the gills are brown to yellow-brown en masse and sometimes include red or pink tones. Most species lack a sipe and instead the pileus attaches directly to the mushroom’s substrate with a small plug of tissue. Some species do form a rudimentary stipe, but they still clearly put much more effort into making the pileus.²

Crepidotus species are usually fan-shaped, but this varies depending on the position of the mushroom on its substrate. Normally, the mushrooms fruit from the side of a log. In this case, the pileus orients itself perpendicular to the log and parallel to the ground. This results in the fan shape. If the surface of the log is irregular or curves, the mushroom will have a bit more space to grow and will acquire a kidney-shape. When a Crepidotus fruits underneath or on top of a log, the mushroom has enough space to make a complete (or nearly complete) circle.²

The most interesting cluster of Crepidotus mushrooms I have found was in a bed of mulch. Unfortunately for the mushrooms, this mulch was fairly flat and they couldn’t find a piece tall enough to fruit parallel to the ground. So, they formed perpendicular to the ground instead. This is not an ideal configuration, but demonstrates why stipes are important. When oriented perpendicular to the ground, a spore that drops from one gill will land on the gill directly below it. Most mushrooms solve this problem by lifting the pileus off the ground with a stipe. Crepidotus species don’t need to do this because they fruit from logs, which are already above the ground. Instead of wasting energy on producing a stipe, they simply fruit directly from the side of the log, which is already above the ground. The energy saved allows the mushroom to produce more spores; it also means the mushroom can’t compensate when it finds itself on a reasonably flat surface.

Identification to Species

Crepidotus is not very well treated in field guides, which is hardly surprising given how boring the genus is. North America has over a hundred species of Crepidotus,³ but only Crepidotus experts can readily identify more than a handful of species. Most people are satisfied with knowing the few “charismatic” species presented in field guides. Identifying any Crepidotus with more accuracy than a field guide can provide requires a microscope, a suitably detailed key, and a lot of patience. The go-to key for Crepidotus is North American species of Crepidotus by Hesler and Smith, but you can also try the other papers listed on this page. When attempting to identify a Crepidotus with a microscope, pay particular attention to the spores, the cystidia on the gill edges, the top layer of the pileus, and the presence or absence of clamp connections.⁴

Edibility

Most species of Crepidotus are considered inedible. Mushrooms in the group are not reported to contain any toxins; they are just too small and thin-fleshed to consider worth eating. Some of the species are listed as “edibility unknown” for the same reason.³ They are too small or unappetizing so nobody eats them and mycologists have no data to assess edibility.¹ You could try eating them at your own risk to fill in some of these knowledge gaps, but it’s probably not worth the effort.

Similar Species

Confusion is most likely to occur with other “pleurotoid” mushrooms.² Pleurotoid means “like Pleurotus” (as in P. ostreatus, the Oyster Mushroom, FFF#021), which also grows on wood, has gills, and has a rudimentary stipe.⁵ There are many mushrooms that fit this general description, including the Crepidotus species. The best way to separate Crepidotus from other pleurotoid mushrooms is by taking a spore print. Nearly all other pleurotoid mushrooms have pale spore prints.² The few brown-spored pleurotoid mushrooms from other genera are larger and/or have more brightly-colored flesh than is normal for Crepidotus species (see, for example, Tapinella panuoides).³

To accurately check whether your brown-spored pleurotoid mushroom belongs to Crepidotus, you will need a microscope. Crepidotus species have spores without a germ pore and usually do not have pleurocystidia.¹ The previous sentence also describes some species of the closely related genus Simocybe. However, those mushrooms can be differentiated because Simocybe fungi produce smooth spores, have lots of cystidia, and often have a greenish tint to the pileus.⁶ Mushrooms in Crepidotus can produce either smooth or bumpy spores, but have fewer cystidia and never have a green tinted pileus.^2,3,6

Taxonomy

Crepidotus is another one of those groups whose taxonomy was revised recently. Prior to 2004, the genus was placed in the family Crepidotaceae along with a few other microscopically similar genera. However, genetic analysis of that family revealed it was polyphyletic, containing mushrooms from three disparate lineages. After 2004, the only two groups left in the Crepidotaceae were Crepidotus and the stipitate genus Simocybe. These two genera are related to one another and both align closely with the genus Inocybe.⁶ Apparently, a family consisting of only two genera was too small to justify keeping the name, since both genera now belong in the family Inocybaceae.^7,8 The stipitate genera that formerly belonged to the Crepidotaceae now key out alongside stropharioid mushrooms or with little brown mushrooms.^6,9

Kingdom	Fungi
Division	Basidiomycota
Subdivision	Agaricomycotina
Class	Agaricomycetes
Subclass	Agaricomycetidae
Order	Agaricales
Family	Inocybaceae
Genus	Crepidotus (Fr.) Staude7