Crimson Cup Identification Guide

What you actually notice first

Almost nobody finds this species by scanning for mushroom shapes. You find it because a patch of colour that has no business existing in February catches the eye: a scatter of small scarlet discs sitting in soaked moss and blackened leaves, the exact red of sealing wax. The setting is nearly always a damp broadleaf woodland — a stream bank, a shaded hollow, the wet ditch beside a woodland track, or the mossy base of an old hedge. The ground squelches. Very often the cups are half buried, so what you see at first is only a red arc breaking the surface of the moss, with the rest of the fruitbody hidden below. That is your cue to stop and clear the litter away by hand: underneath there will almost always be a fallen stick, sodden and usually barkless, with several cups springing from it along its length.

That combination — winter or very early spring, wet ground, a hidden hardwood twig, and a shocking red interior — is most of the identification before you have even picked one.

Step one: read the cup itself

Measure the width. Mature fruitbodies run roughly 1 to 5 cm across, occasionally a little more on a rich piece of wood. Young ones start as almost closed spheres with a small opening, then expand into a deep bowl, then into a shallow saucer, and finally into a nearly flat, often wavy disc when very old.

The inner face is the fertile surface, the hymenium. It should be smooth, matt to very slightly waxy in appearance, without veins, wrinkles, ribs or hairs, and it should be an intense scarlet to vermilion. Specimens fruiting in deep shade or those that have been repeatedly frozen can fade to orange, salmon or even dull ochre, so treat a pale interior as weathering rather than as a different fungus if everything else matches. Look at the rim: young margins are neatly inrolled, older ones flare out, often splitting into a few irregular lobes.

Step two: turn it over

The outside is the character most beginners skip and it is genuinely diagnostic at genus level. The exterior of this cup is pale — whitish, pinkish-buff or very pale flesh colour — a strong contrast with the interior. It is dry and finely downy, and under a hand lens it looks felted, like matted white wool laid over the surface. Those matted hairs are worth a close look because they carry the microscopic character that separates the species within the group.

Run a fingertip over the outer surface. It should feel soft and slightly clinging, never slimy, never granular, and never studded with the stiff dark bristles you get on the eyelash cups.

Step three: stalk, base and attachment

There is a stalk, but it is easy to miss because it is usually buried. Excavate carefully. You should find a short, tapering, whitish stipe anywhere from a couple of millimetres to about three centimetres long, sometimes eccentric rather than central, running down to a small white pad of mycelium that grips the wood. On very buried specimens the stalk elongates to reach the surface, so stalk length is a poor character on its own.

Always follow the stalk to its anchor. If it ends on soil with no wood at all, you are probably not in this genus.

Step four: flesh and colour change

Slice a cup vertically with a sharp blade. The flesh is thin — often barely a millimetre or two — firm, slightly rubbery and a little translucent when wet. In section you see a clean sandwich: a thin red fertile layer on top, a pale layer beneath it. There is no latex, no milk, and no colour change on cutting or on bruising; a cut edge that sat in your pocket for an hour looks the same as it did on the log. Anything that darkens, blues, or exudes liquid is a different fungus.

Step five: taking a print from a cup fungus

Cup fungi are not agarics and they do not drop spores downward, so the usual trick of laying a cap on paper fails. They fire ascospores upward from the inner surface. Two methods work well in practice.

The patient method: rest a fresh cup right way up in a closed container with a strip of black card or a glass slide propped a centimetre or two above the opening, and leave it in a cool place for several hours. A pale film accumulates on the card directly above the hymenium.

The quick method: hold a fresh, well hydrated cup close to your face in still air and breathe warm damp air across it. Often the whole hymenium releases at once in a visible white puff, which you can catch on a slide held above.

The deposit is white to very pale cream, never brown, pink or black. Under a microscope the ascospores are large and unmistakable in shape — smooth, hyaline, and long-elliptical at roughly 26 to 40 micrometres by 10 to 12 — and they sit eight to an ascus in asci that open by a neat hinged lid.

Substrate and season as identification characters

Treat substrate and date as hard evidence, not background detail. This fungus is a wood decayer of fallen broadleaf branches lying in permanently damp conditions. Willow, hazel, elm, beech, maple, sycamore and alder are all common hosts. The wood is usually well rotted, soft to a thumbnail, often stripped of bark, and frequently overgrown by moss.

The season is late autumn through winter into mid spring, with the peak in most temperate regions falling between January and April. A red cup on a summer woodland floor is far more likely to be something else.

Separating it from its look-alikes on structure alone

Its own close relatives. The most honest thing a field guide can tell you is that this species has near-identical siblings, and they are separated by the hairs and the spores rather than by the eye. Pull a few hairs from the outer surface and mount them: hairs that are strongly and repeatedly coiled, like tiny corkscrews, point to a different member of the group, while straight or only gently wavy hairs fit this one. The spores back it up — ends neatly rounded, with two large oil bodies at the poles, versus ends that look flattened or cut off with many small droplets scattered through. A related North American species has an exterior that is distinctly whiter. If you have no lens, record it to genus and be content.

Orange peel fungus. Larger, thinner, brighter orange rather than red, brittle rather than rubbery, with no stalk and no felty exterior, growing directly on bare soil, disturbed ground and path edges, and fruiting in autumn.

Snowbank orange cup. A spring species of conifer country near melting snow, more yellow-orange, and it stains blue-green where handled or aged — a colour change this species never shows.

Eyelash cups. Much smaller, usually under a centimetre, flat rather than bowl-shaped, and ringed with conspicuous stiff black hairs standing out from the margin like lashes.

Long-stalked relatives. Some small red cup fungi sit on a slender, clearly exposed stalk that is longer than the cup is wide, with a much smaller cup, and they fruit in warmer months.

Dark cups. The urns and black cups share the goblet outline but are dark brown to black inside, tough and leathery, and often much larger.

A quick field sequence

Colour inside scarlet, outside pale and felty; cup 1 to 5 cm; short buried whitish stalk; thin unchanging rubbery flesh; attached to a damp buried broadleaf stick; winter to spring; white spore deposit. Tick all seven and you are on solid ground for the genus, and on the commonest member of it in most of its range.