Fairy Inkcap Identification Guide

First Impressions

Nothing else in the woods looks quite like a fresh troop of fairy inkcaps. You come across a decaying stump, or a patch of ground over a buried root, and its surface is covered in hundreds of tiny pale mushrooms — sometimes a thousand — packed shoulder to shoulder in a continuous carpet that flows over and around the wood. The overall impression is of a scattering of small beige and grey thimbles.

Two things stand out immediately. First, the numbers: this species almost never appears as a few individuals. Second, the pleating — even at arm's length, the caps look grooved from margin to centre, like tiny folded parasols.

Timing is part of the character. A troop can appear overnight after warm rain, peak within a day, and be a collapsed grey smear on the wood forty-eight hours later. If you find one in good condition, examine it immediately.

Reading the Cap

Get a lens on a single cap and work through it.

• Size: tiny, 5–15 mm across, occasionally to 20 mm.
• Shape: egg-shaped at first, then bell-shaped to broadly conical, and finally flattening and turning up slightly at the rim in age.
• Colour: pale buff, honey-tan or ochre at the very centre, fading outward through cream to pale grey at the margin. Ageing caps go progressively grey and then blackish at the edge.
• Grooves: the surface is deeply pleated or radially furrowed from the margin almost to the disc, following the lines of the gills beneath. The furrows are visible without a lens and are one of the fastest field characters.
• Hairs: the crucial lens character. The whole cap surface is covered in minute pale hairs (setulae), giving a frosted or finely fuzzy look under magnification. They are colourless to brown and can be seen along the cap edge in silhouette against the sky.

Gills

The gills are narrow and moderately crowded, attached to the stipe or nearly free, and they follow a strict colour sequence with age:

white → pale grey → dark grey → blackish

Because a troop contains caps of every age at once, you can usually see the entire sequence side by side on a single stump, which is a helpful confirmation in itself.

The key point of technique concerns deliquescence. This is an inkcap, but it is a poor one. The gills do not dissolve into thick black ink the way a shaggy inkcap does; they blacken and then the whole small cap withers, collapses and shrivels, at most producing a slight blackish smear. If you are looking at a mushroom that melts into a running black liquid, you are looking at something else.

Stipe and Base

The stipe is 1–4 cm long and barely 1–2 mm thick — thread-like, white to translucent whitish, and very fragile. It is hollow, equal in width or slightly swollen at the base, and covered in the same fine hairs as the cap, best seen at the apex.

Two negative characters matter here:

• No ring and no ring zone. There is no membranous veil on the stipe.
• No volva or bulb. The base is simple, sometimes with a whisper of white mycelium where it enters the wood.

There is also no ozonium — no conspicuous orange-brown felty mat of mycelium on the substrate, which is a feature of some other small inkcaps.

Individual stipes arise separately from the wood rather than being fused into clumps at a common point; the troop is a crowd, not a bouquet.

Flesh and Colour Change

The flesh is barely there: a membranous layer under a millimetre thick, white and watery, with no distinctive smell and no colour change on cutting apart from the ordinary blackening of the gills as spores ripen. Nothing bruises, nothing exudes, and there is no latex.

Handle a cap and it deforms; the entire fruitbody is so delicate that pressing it flat between finger and thumb ruins the specimen. Collect on a piece of the wood itself, or transport in a rigid box.

Taking a Spore Print

These caps are small and short-lived, which makes technique matter.

1. Choose a cap whose gills have gone dark grey to black but which has not yet collapsed.
2. Cut the stipe flush and set the cap gill-side-down on white paper, so the dark print shows clearly.
3. Cover with a small jar; the humidity keeps the cap from shrivelling before it drops.
4. Two to four hours is usually enough; these caps release spores rapidly and then expire.

The print is blackish-brown to black. A useful alternative is to lay a whole cluster of caps on paper overnight and read the combined deposit. In the field you can often see the same thing naturally: mature caps drop spores onto the caps of younger ones below, dusting them dark.

Microscopically the spores are smooth, ellipsoid, dark reddish-brown to blackish in mass, with a central germ pore; the cap surface bears the characteristic setulae.

Substrate, Season and Ecology

The fairy inkcap is a wood-decay saprotroph and its substrate list is narrow and useful:

• decaying hardwood stumps, especially the cut surfaces and the root flare;
• the bases of standing dead or dying broadleaf trunks;
• buried roots and buried wood, which is why the troop sometimes appears to be growing straight out of a lawn or a path with no wood in sight;
• occasionally very rotten sawdust and wood-chip mulch.

It is heavily biased toward broadleaf trees — beech, oak, elm, ash, willow, poplar — and rare on conifers.

Season runs from late spring through autumn, with the biggest flushes in warm, wet weather; in mild climates it can fruit almost year-round. Multiple flushes come from the same stump over successive years as the wood softens.

Ecologically it belongs to the later stages of stump decay, working on wood that is already softened and colonised. The fungus's strategy is visible in the fruiting pattern: it makes an enormous number of very small, short-lived fruitbodies simultaneously, releasing a huge spore load in a single burst rather than maintaining a few long-lived caps.

Separating It From the Look-Alikes

Coprinellus micaceus. The commonest confusion, and it grows in the same places. It is much larger (caps 2–5 cm), warmer tawny-honey to date-brown, and young caps are dusted with glistening mica-like granules. It appears in dense fused clusters of dozens rather than in carpets of hundreds, and its gills genuinely deliquesce into black ink.

Coprinopsis lagopus and relatives. Grey, conspicuously woolly or hairy-fibrillose when young, taller, in small groups, and strongly deliquescent.

Parasola plicatilis and allies. Similar tiny pleated caps, but they grow solitary or in a few scattered individuals in lawns and grassland, not in carpets on wood; the mature cap flattens into a distinct pleated disc with a small darker central plate, and the surface lacks the dense hairs.

Psathyrella pygmaea. Same tiny size, same stumps, sometimes in troops — but the cap is a warmer brown, the pleating is weaker, and the spore print is purple-brown rather than black. This is the one where a print is genuinely necessary.

Small Mycena species on stumps. They can be equally numerous, but the caps are conical rather than pleated to the disc, the gills stay pale and never blacken, and the spore print is white.

Coprinellus domesticus. Larger, and its stump or timber usually carries a conspicuous orange-brown felty mycelial mat at the base.

Field Checklist

• Hundreds of caps at once on or beside a rotting hardwood stump
• Caps 5–15 mm, bell-shaped, deeply pleated to near the centre
• Buff-honey disc grading to pale grey margin
• Fine pale hairs over cap and stipe under a lens
• Gills whitening to grey to black; withering rather than melting into ink
• Thread-thin white fragile stipe, no ring, no basal mat
• Black spore print on white paper
• Late spring to autumn, on hardwood stumps, roots and buried wood