What You Should Know
This mushroom often has an orange shaggy carpet, known as 'ozonium', growing on the surface of the substrate around the stem bases, the Firerug Inkcap is one of several similar species that require careful study to confirm their identities. The ozonium is a very helpful clue, but it is not always present; however, ozonium is much longer-lasting than the inkcap fruitbodies, and so it is often found where there is no evidence of the mushrooms themselves.
If slice a young mushroom in half you will find that the gills are white and are attached to the stipe or free from it. While the pileus expands, the gills darken to grey and eventually turn black and become inky.
This inkcap occurs throughout most of mainland Europe and is also recorded in parts of North America.
Other names: Firerug Inkcap.
Coprinellus domesticus Mushroom Identification
Saprobic, growing gregariously or in small clusters (occasionally alone) on decaying hardwood logs; summer and fall (or overwinter on the West Coast); widely distributed in North America.
To 7 cm across; oval when young, expanding to convex or conical; when young honey yellow and whitish toward the margin, in age gray with a brownish center; covered with whitish to brownish universal veil fragments in the form of small scales or granules; finely grooved or lined from the margin nearly to the center.
Attached to the stem or free from it; white at first, but soon gray, then blackish; eventually deliquescing (turning to black "ink"); close.
4-10 cm long; up to 1 cm thick; equal, with a slightly swollen base; smooth; white; hollow; sometimes with a volva-like rim at the base; usually arising from a mat of orange fibers.
Flesh: Very thin; fragile.
Spore Print: Black or blackish brown.
Coprinellus domesticus Similar Species
Another species, Coprinellus radians, is identical to C. domesticus in almost every respect. C. domesticus and C. radians are the only two species to form an ozonium, so if you find the ozonium you know your mushroom is one of two species. The only difference between the two is spore size: the spores of C. radians grow 8.5-12µm long and 5.5-7µm wide while those of C. domesticus are smaller, growing only 6-10µm long and 3.5-5µm. These species are so similar that some authors consider them to be one and the same.
For most people, differentiating between the two species is impractical – how many people actually have access to a microscope that can be used to measure spore size? If you find only the ozonium or you can’t or don’t have the time to examine the spores, just label the fungus “C.domesticus” or “C. domesticus species group” and be done with it.
There are a couple of other species that appear similar when you ignore the fact that they lack an ozonium. Coprinellus flocculosus is the most similar – it differs only in having a more yellowish-brown cap and a less granular universal veil. Ecology is more helpful for distinguishing the species: C. flocculosus grows on woodchips, straw, sawdust, and other fine plant debris.
Another potential point of confusion is Coprinellus micaceus. This species has distinctive universal veil remnants: the veil breaks up into small shiny mica-like granules. These are usually visible but sometimes wash off completely. C. micaceus also prefers to fruit in dense clusters from the bases of living or dead trees.
Coprinellus domesticus Taxonomy and Etymology
This inkcap mushroom was first described scientifically in 1788 by English botanist James Bolton (1750 - 1799), who gave it the name Agaricus domesticus. Following DNA studies of the former Coprinus group, this species was transferred to the genus Coprinellus in 2001 by American mycologists Rytas J. Vilgalys, John Hopple and Jacques Johnson.
Synonyms of Coprinellus domesticus include Agaricus domesticus Bolton, and Coprinus domesticus (Bolton) Gray.
The generic name Coprinellus indicates that this mushrooms genus is (or was thought to be) closely related to or at least similar to fungi in the genus Coprinus, which literally means 'living on dung' - that's true of quite a few of the inkcaps but not particularly apt for this and several other Coprinellus species. The suffix -ellus indicates fungi that produce fruitbodies that are rather smaller than fruitbodies of Coprinus species.
The specific epithet domesticus comes directly from the Latin domus meaning a house or a home, reflecting the fact that this mushroom sometimes appears on damp flooring or roof timbers. The common name Firerug inkcap refers to the shaggy rug-like orange 'ozinium' that sometimes appears on the substrate from which this inkcap emerges.
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