Grooved Bonnet

Mycena polygramma stands out among bonnets for the toughness and finish of its stem. Where most Mycena have soft, smooth, easily crushed stipes, this species produces a stiff, cartilaginous stalk with a metallic silver-grey sheen, engraved along its whole length with fine parallel grooves or striations — the character preserved in the epithet polygramma, meaning 'many lines'.

The cap is a fairly ordinary conical grey, so identification usually begins with the stem. Fruit bodies appear singly or in small loose groups rather than dense tufts, typically pushing up through soil or leaf litter that conceals the rotting hardwood root or buried stump fragment from which they arise. Excavating carefully will usually reveal a long white rooting base attached to woody material.

It is a common autumn species across temperate broadleaf woodland and one of the larger and longer-lasting bonnets, with fruit bodies that persist for a week or more rather than collapsing in a day.

Cap

The cap is 2–4 cm across, conical to bell-shaped, later broadly convex with a distinct central umbo. The surface is dry to slightly greasy, translucent-striate towards the margin when damp, and grey to grey-brown, occasionally with a faint bluish, olive or lilac tint. Older caps often become paler and develop a slightly wrinkled, wavy margin.

Gills

Gills are adnate with a small decurrent tooth, moderately crowded, whitish at first then greying or picking up a faint pinkish flush with age. The edges remain concolorous — there is no coloured marginal line.

Stipe

The stipe is the key: 5–12 cm tall, 2–4 mm thick, rigid, hollow and cartilaginous, silvery-grey to pale bluish-grey with a slight polished shine, and marked with fine longitudinal grooves and ridges along its entire length. The base is white-downy and characteristically drawn out into a long, rooting extension that runs down to buried wood.

Flesh & spore print

The flesh is thin, greyish-white and rather tough for a bonnet, with little or no distinctive smell. The spore print is white; spores are smooth, ellipsoid and amyloid.

The Grooved Bonnet fruits from decaying hardwood — old stumps, buried roots, fallen branches worked into the soil, and sawdust-rich ground around felled trees. Oak, beech, hornbeam, ash and hazel are all common hosts, and it will also appear along woodland paths and hedge banks where hardwood roots persist below the surface.

Because the wood is usually hidden, fruit bodies often look terrestrial, arising apparently from bare soil or leaf litter. The season runs from August to November, sometimes into December in mild conditions. It is widespread and frequent throughout temperate Europe and occurs across temperate North America and parts of temperate Asia.

Mycena polygramma is a wood saprotroph, causing a slow white rot in buried and surface hardwood debris. Its mycelium colonises root fragments, stump remnants and larger woody pieces in the soil profile, extending rhizomorph-like strands that emerge as the long rooting stipe base of each fruit body.

The species is part of the mid- to late-stage decay community, arriving after primary colonisers have softened the wood. Its comparatively robust fruit bodies stand up well to wind and drying, allowing spore release to continue over several days from the white gills. Repeat fruiting on the same buried stump over successive autumns is typical.

Mycena galericulata is the most frequent confusion: it shares the grey conical cap but is usually tufted on visible stumps, has gills that flush distinctly pink with age, and has a smooth stipe without the fine engraved grooves. Mycena inclinata grows in dense clusters on oak, has a strongly scalloped cap margin and a stipe that is white above and rich orange-brown below.

Mycena vitilis is more slender with a very tough, elastic, smooth stipe and a smaller cap, lacking the silvery grooved finish. Larger grey-brown litter species such as Mycena vulgaris are separated by their slimy stipe surface. In all cases the combination of rigid silvery grooved stem plus long rooting base is decisive for M. polygramma.