Green Pepe Identification Guide

The Setting: Warm, Wet and Usually After Dark

You come across this species in humid subtropical or tropical forest, most often in the days immediately following heavy rain in the warm season. The ground layer is deep with fallen palm petioles, bamboo culms, twigs and rotting branch wood, and the air is close. Two search strategies work. By day, scan pale rotting litter for delicate greyish bonnets barely larger than a fingernail. By night, walk the same ground with your torch off and let your eyes adapt for at least ten minutes; the colony announces itself as a soft green glow at ankle height. Fruit bodies are short-lived, often expanding overnight and collapsing within a day or two, so a productive patch can look empty forty-eight hours later.

First Impression

The overall impression is fragility. A troop of small, translucent, greyish-white bonnets on threadlike stems, clustered on woody debris, with caps that catch the light because they are sticky. Nothing about the fungus is fleshy or substantial; a whole fruit body weighs almost nothing and tears if you pull rather than lift it. Collect by easing the stipe base away from the substrate with a knife so the tiny attachment disc stays intact, because that disc is one of the more useful characters.

Cap: Size, Shape, Surface and Striations

Caps range from about 8 to 30 mm across. They begin hemispherical to bell-shaped and expand to convex and finally almost flat, sometimes with a shallow central depression in age. When fresh and wet the surface is distinctly viscid, even glutinous, and picks up litter fragments. The colour is pale: grey-brown, greyish or fawn towards the centre, fading outwards to nearly white, and the whole cap pales further as it dries. The single most useful cap character is the sculpture. The margin is translucent-striate from an early stage, so you can count the gill positions through the flesh, and with expansion the striations deepen into pronounced radial grooves and furrows that run most of the way to the disc, giving the mature cap a pleated or umbrella-ribbed profile.

Gills and Attachment

Turn the cap over. The gills are adnate, frequently with a short decurrent tooth running a little way down the stipe, and they are relatively broad for the size of the cap. Count roughly seventeen to thirty-two reaching the stipe, with shorter intermediate gills between them. The colour is white to pale grey, sometimes with the faintest greenish cast in fresh material, and the edges are even rather than serrated. Because the flesh is so thin, the gills are the substantial part of the cap and are what you examine first when the specimen has partly collapsed.

Stipe and the Basal Disc

The stipe is 6 to 30 mm long and only 0.3 to 1 mm thick, cylindrical, hollow, smooth and translucent, pale greyish above and often a little darker below. Fresh stipes are viscid to the touch. The character to look for is at the very bottom: the stipe expands abruptly into a small flattened basal disc, roughly 1 to 3 mm across, glued to the twig, culm or petiole. That little suction-pad base is typical of the group and is easily destroyed by careless collecting, so lift it with a blade rather than pinching the stem.

Flesh, Colour Change and Odour

The flesh is watery, translucent and no more than a fraction of a millimetre thick over most of the cap. There is no colour change on cutting or bruising; damaged tissue simply becomes duller and more transparent as it loses water. No latex or coloured juice is present. Odour is negligible or faintly mushroomy and is not a working character here.

Spore Print and Microscopy

A spore print takes patience because the cap is small and dries fast. Cut the stipe just below the gills, set the cap gills down on black card or a glass slide, cover it with an upturned cup with a damp tissue inside, and leave it for two to four hours. The deposit is white. Under the microscope the spores are smooth, broadly ellipsoid, roughly 7 to 8.5 by 5 to 6 micrometres, and amyloid, meaning they turn blue-grey in Melzer reagent, which places the collection in Mycena and excludes several superficially similar white-spored genera. The cap surface is a gelatinised layer of hyphae, which is why the cap is sticky, and the gill-edge cystidia are club-shaped.

Bioluminescence as a Structural Character

The green glow is a genuine identification character and should be recorded rather than dismissed as a curiosity. Light is emitted mainly from the gills and, more weakly, from the cap surface and stipe, in a pale green shade. It is strongest in freshly expanded caps and fades markedly as the cap flattens and the fruit body starts to collapse, so an old specimen may not glow at all. To assess it, sit in complete darkness for ten to fifteen minutes without looking at any screen or torch, then examine the collection; a long camera exposure of twenty seconds or more will record glow that the eye barely resolves.

Substrate and Season

The fungus is a litter and wood decomposer. Typical substrates are decaying bamboo, fallen palm petioles and fibrous sheaths, small dead branches and accumulated leaf litter on the forest floor, usually in shaded, undisturbed, permanently humid situations. Fruiting is strongly seasonal and rain-triggered, concentrated in the warm wet months, and often occurs in flushes where dozens of fruit bodies appear across a single decaying culm at once. Records centre on East and Southeast Asia and the western Pacific, extending to parts of Australia and the Indian Ocean islands.

Separating It From Look-alikes on Morphology Alone

Other luminous fungi are the first hurdle. Filoboletus manipularis has a spore-bearing surface of fine pores rather than gills, which settles it instantly with a lens. Panellus stipticus is tough and leathery, kidney-shaped, attached sideways to wood with little or no stipe, and brownish with a dry felted cap. Mycena lux-coeli and its relatives are close, and separation rests on details such as gelatinisation of the stipe, cap colour and spore dimensions rather than on the presence of glow. Mycena luxaeterna has a conspicuously gelatinous, jelly-coated stipe.

Among non-luminous small agarics, other Mycena species in the same habitat generally lack the combination of a viscid cap, deep radial furrows and a distinct flattened basal disc; many have dry caps, coloured gill edges or a rooting base. Marasmius species have tough, wiry, often dark and shining stipes that revive after drying, dry non-viscid caps, and no basal disc. Small Crepidotus species are laterally attached with brown spore deposits. If the collection is white-spored, viscid, deeply grooved and pad-footed on bamboo or palm debris, you are on firm ground.