Blackedge Bonnet

Mycena pelianthina is one of the larger and more solid bonnets, closer in build to Mycena pura than to the hair-stemmed litter species. Its calling card is the gill edge: with a hand lens, every gill shows a crisp dark purple-brown to blackish border against a much paler violaceous face, a pattern created by densely packed pigmented cheilocystidia.

The cap is a soft lilac-brown to pinkish-grey that fades as it dries, and the whole fruit body carries a strong, penetrating radish-like smell that is often noticeable before the mushroom is picked up. Fruit bodies appear in loose troops or small arcs across deep leaf litter, sometimes in impressive numbers under mature beech.

Within the genus, it belongs to a group of larger, non-bleeding, litter-dwelling bonnets with violaceous and pink pigments, of which M. pura is the best-known member. The dark gill margin is the single character that most cleanly sets M. pelianthina apart from all of them.

Cap

The cap is 2–5 cm across, convex to broadly bell-shaped, later flattening with a shallow umbo or a slightly depressed centre. The surface is smooth, moist and faintly translucent-striate at the margin, coloured lilac-brown, pinkish-grey or dull violaceous-brown, hygrophanous and fading to pale pinkish-buff from the centre outwards as it loses moisture.

Gills

Gills are adnate to slightly sinuate, moderately crowded, and pale lilac, greyish-violet or pinkish-grey. Each gill is bordered by a distinct, continuous dark purple-brown to almost black edge — the defining character, easily seen with a hand lens and often visible to the naked eye on fresh specimens.

Stipe

The stipe is 3–8 cm tall and 3–6 mm thick, hollow, cylindrical, smooth or finely fibrillose, coloured pale lilac to pinkish-grey and usually paler than the cap. The base is often slightly swollen and clothed in coarse white mycelial down that binds leaf litter to it.

Flesh & spore print

The flesh is thin, pallid to faintly lilac, with a strong and persistent radish-like odour. The spore print is white; spores are smooth, ellipsoid and amyloid.

Blackedge Bonnet fruits in deep leaf litter under broadleaf trees, with a marked preference for beech on base-rich or calcareous soils. It also appears under hornbeam, oak, ash and hazel where the litter layer is deep and the ground is neutral to alkaline.

Fruit bodies emerge in scattered troops, lines or partial rings across the litter, sometimes in large numbers where conditions suit. The season runs from July or August through to November. The species is widespread in temperate Europe, frequent in the beechwood belt, and is also recorded across temperate North America and parts of Asia.

This is a litter saprotroph, breaking down fallen leaves, petioles and fine plant debris in the upper humus horizon. Its mycelium spreads as an extensive sheet through the litter, which is why fruit bodies often appear in troops or arcs marking the outward growth of a colony.

The combination of a relatively fleshy fruit body and a deep, moisture-holding litter layer allows the species to fruit for longer than the more ephemeral small bonnets, with individual mushrooms lasting a week or more. As with other beech-litter specialists, it contributes to the slow decomposition of waxy, decay-resistant leaves and helps recycle nutrients back into the woodland soil.

Mycena pura is the closest match in size, colour and radish smell, but its gills are uniformly pale lilac or pink with no dark marginal line — checking the gill edge with a lens resolves the pair immediately. M. pura also shows a wider colour range, from lilac through pink to almost white.

Mycena rosea is larger with a distinctly rosy-pink cap and, again, plain gill edges. Mycena pelianthina's dark-edged gills can superficially recall Mycena aurantiomarginata, but that species has a brownish-olive cap with bright orange rather than blackish gill edges and fruits in conifer needles. Larger grey litter bonnets such as Mycena galericulata lack any violaceous tone and grow on wood.