Green Elf Cup Identification Guide

The Wood Announces It First

Nine finds out of ten begin with the stain rather than the fungus. Working through a damp broadleaf wood in late summer or autumn, you roll over a barkless fallen branch or break open a soft, pale, well rotted log, and part of the wood inside is coloured an improbable blue-green, somewhere between verdigris and weathered copper sheeting. The colour runs with the grain in streaks and zones and is often fenced in by thin dark demarcation lines laid down where this fungus met a competing one. That stained timber is the signature of Chlorociboria aeruginascens, and it can sit in a log for years after any fruit bodies have come and gone. Learn the stain first; the cups follow.

What You Are Looking At Once You Kneel Down

The fruit bodies are apothecia, tiny open discs, and they are small enough that most walkers pass them without registering them at all. Expect 1 to 5 mm across, occasionally 8 mm on a very wet log, scattered by the dozen or the hundred over a stained surface. Fresh ones are shallow bowls with an inrolled edge; as they mature they open out flat, then become wavy, lobed or saddle-shaped, so a single patch usually shows several outlines at once. The colour is a saturated blue-green that no other small disc on wood quite matches, and it is even across the disc rather than zoned.

Reading the Disc, Margin and Outer Surface

Put a hand lens on a single apothecium. The upper surface, the spore-bearing hymenium, is smooth, faintly shining when moist, and flat to gently concave. The margin is thin, sometimes minutely toothed or torn in older discs, and often a shade paler than the centre. Turn the cup over. The outer surface is duller, minutely downy or granular under magnification, and usually a paler blue-green with yellowish or ochre tints creeping in as the fruit body ages. Those yellow tones on the outside are ordinary maturity rather than a second species growing alongside.

Stalk, Attachment and Habit

Each disc sits on a short stalk, typically 0.5 to 3 mm long and often shorter than the disc is wide. The stalk is usually attached off-centre or almost laterally, which is why the discs so often look tilted or spoon-shaped instead of sitting upright like little goblets. It is the same colour as the cup or slightly darker, and it plugs straight into the wood with no visible basal pad. Habit is part of the picture: this is a gregarious fungus, and a good colony forms an irregular sheet of discs across bare damp wood, sometimes crowded enough that neighbouring margins deform one another.

Texture, Section and Drying Behaviour

Fresh material is soft, rubbery and slightly gelatinous. A disc pinched between finger and thumb springs back rather than crumbling. Cut one in half with a razor blade under the lens and the section is thin, waxy and uniformly coloured, with no obvious layering to the naked eye. There is no bruising reaction worth recording, and that absence is itself useful, because handling does not shift the surface to another colour. Drying is where the real change happens: as material dries the discs contract, curl inward, darken and take on duller or greener tones, then swell and recover much of their fresh look when rewetted. Shrivelled material on a log is always worth a splash of water and ten minutes of patience.

Getting a Spore Deposit From a Cup Fungus

Cup fungi do not drop spores passively the way gilled fungi do, they shoot them, so the technique differs from a standard spore print. Cut a small piece of stained wood carrying several fresh apothecia, invert it a few millimetres above a clean glass slide or a square of dark card, and enclose the whole arrangement in a closed box with a drop of water to keep the air humid. Within a few hours the asci discharge and leave a faint whitish film, easily overlooked on white paper, which is why glass or dark card earns its place. Under the microscope the spores are small, colourless, smooth and narrowly spindle-shaped, roughly 5 to 8 micrometres long by 1 to 2 micrometres wide, frequently with a minute oil droplet at each end. The asci hold eight spores and have an apical pore that colours blue in iodine solution; the paraphyses between them are slender threads that may carry green pigment.

Substrate and Season

This is a decomposer of broadleaf wood. Search oak, ash, hazel, birch, beech and willow, on fallen branches and small logs that have shed their bark and reached the soft, pale, easily dented stage of decay. Shade and humidity are essential, so ditch bottoms, stream banks, north-facing slopes and the interiors of dense woodland outproduce open sun-dried brash piles by a wide margin. Apothecia appear mainly from mid summer through autumn and, in mild oceanic climates, well into winter, always following a wet spell. Conifer wood is not typical habitat, so a blue-green stain in pine deserves a second look.

Separating It From Look-alikes on Structure Alone

The one genuine difficulty is Chlorociboria aeruginosa, which is macroscopically almost the same fungus. The honest position is that separation is microscopic: C. aeruginosa has distinctly larger spores, commonly 9 to 15 micrometres long and 2 to 4 micrometres wide, against the short narrow spores described above. Macroscopically it tends towards better developed stalks, deeper and less flattened discs, and an outer surface that contrasts more strongly with the hymenium, but these are tendencies, not rules, and a single collection should not be named on them.

Everything else is straightforward. Bisporella citrina is bright lemon yellow and effectively stalkless. Ascocoryne sarcoides is purple, gelatinous and forms lumpy cushions rather than tidy stalked discs. Chlorencoelia versiformis is larger, olive to olive-brown rather than turquoise, and leaves no colour in the wood beneath it. Green algal films and orange-green Trentepohlia growths on damp bark are flat and structureless, smear when rubbed, and never produce discrete discs. Finally, remember that the blue-green stain identifies the genus and not the species, so wood without fruit bodies should be recorded only as Chlorociboria.

A Working Sequence in the Field

Find stained wood; check that the colour penetrates the wood rather than sitting on the surface; scan every face of the piece with a lens, wet and dry alike; confirm that the discs are stalked, blue-green on both surfaces, rubbery and gregarious; note that the host is a broadleaf. Everything to that point gives you the genus with real confidence. A short spore discharge at home settles the rest.