Green Pepe

Green Pepe (Mycena chlorophos) is one of the best known bioluminescent agarics, widely photographed in Japan, Taiwan, Southeast Asia, Australia and parts of Brazil. It belongs to Mycena, an enormous genus of small, fragile, white-spored mushrooms with conical to bell-shaped caps and slender, cartilaginous stipes. Only a small fraction of Mycena species glow, and M. chlorophos is among the brightest.

By day the mushroom is easy to overlook: a pale grey to greyish-brown disc barely a couple of centimetres across, slick with a gelatinous film, perched on a thread-thin stem. By night the gills, the top of the stipe and the basal disc give off a steady green glow that is strongest in freshly expanded fruit bodies and fades within a day or two as the mushroom collapses.

What makes it distinctive is the combination of extreme fragility, a viscid translucent cap surface with a grooved margin, an attached basal disc that anchors it to woody litter, and the glow itself. The light is produced by a luciferin-luciferase reaction in living tissue, so it dims quickly once the fruit body begins to dry or decay.

Cap

Small, 8-30 mm across, at first a rounded bell or hemisphere, expanding to broadly convex or nearly flat with a shallow central depression. The surface is sticky to slimy when moist, translucent enough that the gill lines show through as radial grooves running almost to the centre. Colour is pale greyish-brown to olive-grey at the disc, fading to whitish or very pale grey at the thin, often scalloped margin.

Gills

Adnate to slightly notched, moderately spaced, whitish to pale grey, narrow, with the edges sometimes appearing slightly gelatinous. In darkness the gill faces are the main source of the green light. Short intermediate gills are present between the full-length ones.

Stipe

Thread-like, 6-30 mm long and only about 1 mm thick, hollow, translucent grey to pale brownish, smooth or minutely dusted, and glowing near the apex. The base sits on a small flattened, disc-like pad of tissue attached to the substrate, a useful field feature.

Flesh and spore print

Flesh is almost non-existent, watery and translucent, without colour change when cut. The spore print is white. Fruit bodies are so delicate that they wilt within hours of picking or drying.

Green Pepe is a warm-climate litter and wood decomposer, fruiting on dead palm fronds and petioles, bamboo culms and sheaths, fallen twigs, bark fragments and rotting logs in humid subtropical and tropical forest. It is strongly tied to humidity: fruit bodies appear in flushes a day or two after heavy rain when night temperatures stay warm, and vanish just as fast in dry spells.

It is recorded from Japan (notably Hachijo-jima and the Ryukyu Islands), Taiwan, China, the Philippines, Malaysia, Indonesia, Sri Lanka, Polynesia, tropical Australia and Brazil. Locally it can be abundant, with dozens of fruit bodies scattered across a single decomposing frond.

The species is saprophytic, breaking down lignin- and cellulose-rich plant debris, especially the tough fibrous tissue of palms and bamboo. Its mycelium permeates damp litter and can itself glow faintly in colonised wood.

The glow is thought to function as an attractant, drawing nocturnal insects that walk over the gills and carry spores away on their bodies, a dispersal strategy that works alongside ordinary wind release. Light output follows a circadian rhythm, peaking at night and dimming toward dawn, and it is strongest in mushrooms that have just expanded their caps.

Other glowing agarics can be told apart by size and structure. Mycena lux-coeli of Japan is similar in stature but has a paler, more translucent cap and a distinctly hairy stipe base rather than a smooth basal disc. Filoboletus manipularis, another tropical glower, has a pored underside instead of gills. Panellus stipticus is fan-shaped and grows in shelving tiers directly from wood with a stub-like lateral stipe or none at all, quite unlike the central thread-thin stem of Green Pepe.

Among non-glowing species, Mycena epipterygia also has a viscid cap and slimy stipe but is yellowish-olive with a peelable elastic pellicle and lacks the basal disc. Small Marasmius species on similar litter have dry, non-viscid, tough caps that revive after drying, and their gills never glow.