Green Elfcup Identification Guide

Where the Search Begins

This fungus rewards a particular kind of searching: slow, low to the ground, and concentrated on dead wood that has already gone soft. The green elfcup colours the timber it inhabits a strong turquoise, a property known for centuries to woodworkers who prized naturally coloured green oak for inlay work. That pigment is your search image. In a wet deciduous wood you scan for pale, barkless branch wood and then look for any hint of blue-green where the surface has weathered or split. Once a stained piece is in your hands, the actual fruit bodies are found by systematic examination of every face with a lens, because they are only millimetres across and frequently hide on undersides pressed against wet leaf litter.

What You See at Arm's Length

Before magnification, a fruiting colony reads as a scatter of tiny blue-green flecks, as though someone had flicked verdigris paint across the log. There may be a handful of them or several hundred packed close together. The individual objects look like miniature discs or shallow saucers rather than pimples, blobs or crusts, and that flatness with a defined rim is the first structural clue that you are dealing with a disc fungus and not a mould, an alga or a slime mould.

Close Reading of the Cup

Under a lens, take one apothecium at a time. Diameter typically falls between 1 and 5 mm. The fertile upper face is smooth and slightly glossy while moist, gently dished when young and flattening or becoming irregularly undulating with age. The rim is thin, entire at first and often minutely ragged later. Flip the disc: the sterile underside is matt, very finely felted, generally paler, and often shows warmer yellow-green or ochre notes as the fruit body matures. A useful discipline is to record both faces separately in your notes, because the contrast between them is one of the few macroscopic characters available in this genus.

Stalk, Attachment and Habit

The stalk is short, often only a fraction of a millimetre to about 3 mm, and its point of insertion is typically eccentric or lateral rather than exactly central. This produces the characteristic lopsided, spoon-like profile visible when you look at a colony from the side. Stalks arise directly from the stained wood surface, sometimes from a shallow crack or the cut end of a branch where the pigmented tissue is exposed. Gregarious growth is the norm, and dense colonies distort one another into angular outlines where the margins press together.

Texture, Section and Drying Behaviour

Fresh apothecia feel rubbery and faintly gelatinous, deforming under pressure and returning to shape. A vertical section under the lens shows a thin, homogeneous, waxy structure with the green pigment distributed through it. Bruising produces no colour shift, and cutting produces no seeping fluid. Drying, on the other hand, transforms the collection completely: the discs shrink, roll inwards, darken, and can look like nothing more than dark specks on a green stain. Because rehydration restores them, dry-looking material should be moistened and left in a closed container for a quarter of an hour before you conclude that a log is not fruiting.

Making a Spore Deposit and What to Measure

A classic spore print, cap down on paper, has no equivalent here, so use a discharge chamber instead. Trim a chip of colonised wood bearing several plump, fresh discs. Suspend or prop it so the fertile faces point down towards a glass slide two or three millimetres below, then seal everything in a lidded box containing a damp tissue. Asci fire their spores upward and outward, and after a few hours a faint whitish bloom accumulates on the slide. Examine it at high magnification. Spores of this species are colourless, smooth-walled, narrowly fusiform and small, most falling between 5 and 8 micrometres in length and 1 to 2 micrometres in width, commonly with a tiny droplet at each pole. Asci are cylindric-clavate with eight spores and a pore that stains blue in iodine; the sterile paraphyses are thin and thread-like. Measuring twenty spores rather than three is the difference between a name and a guess.

Wood, Decay Stage and Season

The fungus works broadleaf timber, most often oak, ash, hazel, birch, beech and willow, and it favours pieces that have already been colonised for some years. The productive decay class is bark-free, pale, soft enough to be scored with a fingernail, and sitting in contact with damp ground or moss. Continuous humidity matters more than warmth: sheltered valley woodland, shaded ditches and the north side of a bank produce colonies long after exposed brash has dried out. Fruiting concentrates in late summer and autumn and continues through mild damp winters, always keyed to recent rainfall. Coniferous substrates are exceptional and should prompt a careful re-examination.

Telling It Apart by Structure Alone

The sister species Chlorociboria aeruginosa is the real test. Colour, habit, stain and substrate all overlap, so macroscopic separation is unsatisfying: at best, C. aeruginosa averages a longer and better formed stalk, a deeper and more persistently cup-shaped disc, and a more sharply contrasting outer surface. The decisive character is spore length. Where this species sits around 5 to 8 micrometres, C. aeruginosa runs roughly 9 to 15 micrometres and is noticeably broader. If no microscope is available, the correct record is Chlorociboria species and nothing more precise.

Other candidates fall away quickly. Bisporella citrina forms crowded yellow discs and never stains its substrate turquoise. Ascocoryne species are purple to pinkish and build gelatinous cushions and blobs rather than stalked plates. Chlorencoelia versiformis is several times larger, olive-brown, and leaves clean wood behind. Green films of algae and Trentepohlia smear when rubbed and lack any disc structure or rim. Small green lichen thalli on the same log have a crustose or leafy body and any fruiting structures they bear are embedded in that body rather than stalked and free-standing.

Field Checklist

Stained wood, colour penetrating rather than superficial, broadleaf host, soft decay class, damp shaded position, discs 1 to 5 mm, stalked and eccentric, blue-green on both faces with a paler downy underside, rubbery texture, gregarious habit, spores narrow and short. Tick those and you have made the identification as far as field characters allow, with the spore measurement completing it.