Magpie Inkcap Identification Guide

A Fungus You Have to Catch in Time

Autumn, a beech wood on chalk, deep drifts of leaf litter under a closed canopy. Standing clear of the leaves is something tall and narrow and dark, 15 to 25 cm high, with a cap shaped like an egg or a thimble, blackish-brown and scattered with irregular white patches. The pattern gives the fungus its name, and at a glance it looks like nothing else in the litter.

The practical problem is time. This is an inkcap, and the fruit body destroys itself as it matures. A cap that is perfect at dawn can be a black dribble on a bare stem by mid-afternoon, and a stem that stood yesterday may be a collapsed thread today. If you find one in good condition, work through the characters immediately and photograph as you go. If you find only ruins, look around: the species often produces a small succession at the same spot, and a younger one is frequently within a metre or two.

The Cap and Its White Patches

Young caps are ovoid to cylindrical, 4 to 8 cm tall and narrower than they are high, sitting on the stem like an acorn in its cup. They expand upward and outward into a conical or bell shape, then the margin lifts, splits and rolls back before dissolving.

The ground colour is dark: sepia, umber, blackish-brown, sometimes with a warmer chestnut tone in the middle. Over this, when young, lies a continuous whitish universal veil, which as the cap expands tears into large, felty, irregular patches and plates. The contrast of white patches on a dark ground is the diagnostic pattern, and it is worth registering how those patches sit: they are loose, superficial and easily knocked off, not scales cut from the cap surface itself.

Because the patches are superficial, heavy rain removes them. A weathered specimen may be almost uniformly dark brown with only a few tatters of white near the apex, and at that point the tall stature, the crowded blackening gills and the habitat carry the identification instead. Between the patches, the cap surface is finely fibrillose and often faintly grooved towards the margin.

Gills and Autodigestion

Cut a young unopened cap in half lengthways rather than trying to peer underneath. The gills are free of the stem, extremely crowded, narrow, and packed in a dense parallel array. There is no ring on the stem, though occasionally a fragile band of veil tissue clings low down.

The colour sequence is fast: whitish or pale grey at first, then grey, then jet black as the spores mature, and then liquid. Autodigestion starts at the cap margin and works inward and upward, so a half-mature cap shows a clean white zone at the top of the gills, a black band below it, and a fringe of black drips at the rim. That inky liquid is loaded with spores and stains anything it touches.

Stem and Base

The stem is the reason this species stands out from the litter: 15 to 30 cm long and only 6 to 15 mm thick, straight or slightly curved, white, hollow, and tapering gradually upward from a slightly swollen or bulbous base.

Its surface is clothed in fine woolly white fibrils that rub off on your fingers, giving a shaggy appearance especially towards the base. Look carefully at the very bottom: there may be loose veil remnants and a shallow rim, but there is never a membranous sac or cup. The stem snaps easily and is often kinked from pushing up through packed leaves.

Flesh, Smell and Colour Change

The flesh is very thin, whitish to greyish, and watery. There is no colour change on cutting in the usual sense; what this fungus does instead is dissolve. Over a few hours, enzymes break the gill tissue down into black liquid, and the process cannot be stopped once started, which is why fresh material must be examined at once and why herbarium collections of inkcaps are usually poor.

The smell of fresh material is distinctive and often described as tarry, naphthalene-like or reminiscent of mothballs. It is a genuinely helpful supporting character on a fresh cap.

Getting a Spore Print Before the Cap Dissolves

The standard overnight print is useless here. Take a cap at the moment the margin begins to lift and before any liquid appears, cut the stem off flush, set the cap gills-down on white paper, cover it, and check after thirty to sixty minutes. You will get a dense deposit that is somewhere between a print and a wash of black ink.

The print is black. Under a microscope the spores are large for the family, roughly 13 to 19 µm long, blackish-brown, lemon-shaped or almond-shaped with a pointed end, and carrying a distinct germ pore. That size is one of the easiest microscopic checks in the group and separates picacea from most of its grey relatives at once.

Habitat, Substrate and Season

Coprinopsis picacea is a litter and buried-wood saprotroph of broadleaf woodland. Its strongest association is with beech on calcareous soils, where it comes up through deep leaf litter, often on shaded banks or along the edges of hollow ways. Hornbeam and oak on chalk also produce records.

Unlike many of its relatives, it is not a dung fungus and not a garden or wood-chip species; if you are standing on a compost heap or a mulched bed, other Coprinopsis are far more likely. It fruits from late summer to late autumn, usually singly or in twos and threes, and it is nowhere abundant. Repeat visits to a known beech bank in October pay better than random searching.

Separating the Close Look-Alikes

Coprinopsis atramentaria is the common large grey inkcap. It is grey-brown, lacks white veil patches entirely, has a smoother cap that is scurfy only over the centre, is shorter and stouter, and typically grows in clustered tufts from buried wood, stumps and disturbed ground rather than singly in beech litter.

Coprinus comatus, the Shaggy Inkcap, is white rather than dark, cylindrical and much longer than wide, and its shagginess comes from recurved scales cut out of the cap surface itself, arranged in concentric rows, not from loose white patches over a dark ground. It also carries a free, movable ring on the stem and grows in grassland, verges and disturbed soil.

Coprinopsis lagopus and its relatives are grey, densely covered in fine white hairs when very young, extremely slender and short-lived, and generally found on wood chips or rich soil. They are much smaller, the white covering is hairy rather than patchy, and the whole cap can vanish within a morning.

Coprinopsis nivea and other white species on dung are uniformly powdery-white and grow directly on animal droppings.

Amanita species carry white veil patches on a coloured cap, which is the one genuine source of confusion at a glance, but their gills are white and do not dissolve, they leave a white spore print, and the stem base sits in a volva. Cutting a fruit body in half and waiting an hour resolves it.

The Combination to Look For

Dark cap ground, discrete felty white patches, extreme height relative to width, hollow shaggy white stem, crowded free gills going black and then liquid, beech litter on chalk in autumn. No other British or European inkcap assembles that set.