#192: Coprinellus micaceus, The Mica Cap

Coprinellus micaceus, commonly known as “The Mica Cap” or “The Glistening Inkcap” is one of the rare inky caps (FFF#177) that is easy to identify. These medium-sized mushrooms appear in dense clusters on dead wood and feature brown caps coated with a distinctive dusting of salt-like or mica-like granules (hence the scientific and common names). Mica Caps are beautiful when young, since the shiny granules make it look like fairy dust was lightly sprinkled over the mushrooms. The unique combination of size, habitat, and fairy dust makes C. micaceus instantly recognizable.

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Description

C. micaceus mushrooms are for the most part umbrella-shaped, although they tend to be a bit rounder at the top than most umbrellas. The mushrooms grow larger than many inky caps, reaching sizes of 2-6cm wide and 2-8cm tall and sometimes even bigger. You usually find Mica Caps growing in large and dense clusters that make these otherwise drab mushrooms easy to spot.^1–4

The pileus is the most important part of C. micaceus for identification. At first, the pileus is ovoid but it soon expands like an umbrella to become convex or somewhat bell-shaped.^1–4 I find that the pileus is usually a bit irregular; it often has a few radial wrinkles that divide it into faint lobes. The cap is some shade of light brown, from yellow-brown to red-brown. This color is deepest at the center of the pileus and gradually becomes paler toward the edge. As the mushroom matures, the colors fade to pale brown and can even become grayish if the gills underneath are mature. One of the most conspicuous features of the pileus is the grooves that extend from the margin to near the center.^1–4

If you look closer, you will see that the entire surface is covered with shiny white granules that are reminiscent of tiny flakes of salt or mica. These granules are the remains of the mushroom’s universal veil, so they start out close together and easy to see but as the mushroom ages they move farther apart. The granules are not attached to the pileus and slough off very easily; a little rain quickly washes off the granules. Thankfully, the Mica Cap’s propensity for fruiting in clusters means that some part of at least one mushroom is usually protected from the rain. No other inky caps have a universal veil that leaves such tiny granules, so it’s very easy to identify C. micaceus when the granules are present.^1–4

Underneath the pileus, the Mica Cap produces gills that radiate out from a central stipe. The gills can be attached or free from the stipe and start out whitish but darken to brown and eventually to black as the mushroom ages. Once the gills are mature, they deliquesce from the edges inward, which turns most – but usually not all – of the cap into inky black goo. The resulting “ink” is teeming with black spores, which give the ink its dark color.^1–4

The stipe is the most boring part of the Mica Cap. It is long, thin, white, and smooth. Sometimes, it takes on some brownish color (especially near the base) or is covered with tiny hairs or granules. There is no evidence of a ring or ring zone on the stipe, which helps separate C. micaceus from many similar inky caps. The stipe is fibrous and hollow, which makes it feel rather flimsy.^1–5

Ecology

C. micaceus is saprobic and gets its energy by decomposing wood. Its favorite meals are stumps, logs, and buried wood.^1–4 Most of the time, the mushrooms grow on wood or right next to wood. I usually find them directly at the bases of trees, even when the trees seem healthy. When it grows from buried wood, the mushrooms fruit directly from the ground. The Mica Cap is not very picky about the type of wood it decomposes, which is unusual in the mushroom world.^1–4

The Mica Cap is a common mushroom in North America and Europe but also grows in more limited areas of South America, Asia, and Australia.² Although it evolved to live in forests, C. micaceus does well in urban landscapes and is a common sight in gardens and cultivated areas. You can find this mushroom in spring, summer, and fall and occasionally in winter.¹ In my experience, it is one of the first gilled mushrooms to appear after the end of winter.

Similar Species

There are many brownish inky caps out there, but the habitat and morphology of C. micaceus easily separate it from look-alikes. Its growth on wood readily distinguishes it from the many inky caps grow on manure, straw, and similar nitrogen-rich habitats (unless C. micaceus is being difficult and growing from buried wood in a manured lawn). Its medium size and clustered growth also eliminate many small (less than 3cm across when mature) or solitary species.⁵ The mushroom most similar to C. micaceus is probably Coprinopsis atramentaria. However, that mushroom is larger, darker brown, and lacks the mica-like granules.^5,6

Edibility

The Mica Cap is considered an edible mushroom, although it does not have much flavor.^2,3,6 Of course, you should collect only specimens that have not yet begun to liquefy.⁶ The inky ones are hard to transport and do nothing for your dish other than make a big mess. Also, be prepared to cook them very soon, as Mica Caps deliquesce quickly.³ Since they have such a bland flavor, you can add them to just about anything. In that respect, C. micaceus is like a thinner version of the button mushrooms (Agaricus bisporus, FFF#002) you find at the grocery store. Because they are rather thin-fleshed mushrooms, you need a lot of them to make a decent dish. Thankfully, the mushrooms usually fruit in large clusters, often with caps at various stages of maturity. This makes it easy to find large enough quantities of young mushrooms.

Taxonomy

C. micaceus may be listed as Coprinus micaceus in older field guides. Coprinus once included all inky caps, but mycologists eventually split the genus up based on microscopic and genetic differences.^2,4,6 Coprinus now contains only relatives of the Shaggy Mane (Coprinus comatus), which belong to a different lineage than most inky caps.² Along with the bulk of the inky caps, the Mica Cap belongs to the family Psathyrellaceae. Read more about inky cap taxonomy on FFF#177.

Kingdom	Fungi
Division (Phylum)	Basidiomycota
Subdivision (Subphylum)	Agaricomycotina
Class	Agaricomycetes
Subclass	Agaricomycetidae
Order	Agaricales
Family	Psathyrellaceae
Genus	Coprinellus
Species	Coprinellus micaceus (Bull.) Vilgalys, Hopple & Jacq. Johnson7