Scarlet Bonnet

Mycena adonis — also treated in modern classifications as Atheniella adonis — is a delicate pink-red bonnet that provides one of the more welcome flashes of colour in autumn moss carpets. The cap begins a saturated coral-pink to scarlet, then bleaches steadily with age and sun exposure through salmon and apricot to almost buff, so a single troop may show a whole gradient of shades.

Unlike the twig-dwelling Mycena acicula, this species is a ground fungus, threading its mycelium through moss cushions, grass thatch and needle litter. It is also distinguished by having a pale, whitish to pinkish stipe rather than a coloured yellow one, so the colour is essentially confined to the cap.

The segregate genus Atheniella was erected for a small group of brightly coloured bonnets with particular microscopic features, and adonis is its type species — a useful thing to know when reconciling older field guides with newer checklists.

Cap

The cap is 5–15 mm across, conical to bell-shaped at first and expanding to broadly convex with a low umbo. The surface is smooth, moist, translucent-striate towards the margin, and a clear coral-pink, salmon-scarlet or orange-red when fresh, fading noticeably towards pale pinkish-buff or almost whitish as the fruit body ages.

Gills

Gills are adnate to narrowly adnexed, rather distant, and whitish to pale pink, sometimes taking a faint apricot tone near the cap margin. The edges are concolorous, without a contrasting dark or coloured marginal line.

Stipe

The stipe is 2–6 cm tall and about 1 mm thick, hollow, smooth and fragile, coloured white to pale pinkish or very pale yellowish, sometimes with a faint flush near the apex. The base carries a few fine white hairs but is not conspicuously rooting.

Flesh & spore print

The flesh is extremely thin, pale pinkish and watery, with no notable smell. The spore print is white; spores are smooth and ellipsoid.

Scarlet Bonnet fruits on the ground among mosses, short grass thatch, heather litter and fallen conifer needles. It favours damp, open situations — the mossy edges of conifer plantations, wet heaths, dune slacks, boggy grassland and streamside banks — as well as needle litter inside spruce and pine woodland.

The main season runs from August through October, extending later in mild coastal areas. It is widespread across northern and temperate Europe and occurs across the boreal and temperate zones of North America and Asia, generally being commoner in cool, high-rainfall regions with abundant bryophyte cover.

The species is a saprotroph of fine ground litter, decomposing moss stems, dead grass leaves, needles and small plant fragments in the surface humus. Its role sits alongside other small litter fungi in the early breakdown of soft plant tissue, working at a scale far below that of the larger wood-rotting fungi.

Because bryophyte carpets buffer moisture, the fungus can fruit reliably in habitats that dry out at the surface, and troops often reappear in the same moss patch across seasons. The delicate fruit bodies persist only a few days, releasing white spores into the near-ground airflow before collapsing.

Mycena acicula is comparably bright but has an orange to scarlet-orange cap combined with a distinctly yellow stipe, and grows on fallen twigs rather than in moss. Mycena flavoalba shares the moss and grass habitat and general shape but is ivory to pale primrose-yellow, entirely lacking pink or scarlet tones.

Mycena rosella has a pink cap but is separated by gills with distinctly darker pinkish-red edges and a preference for conifer needle beds. Faded specimens of M. adonis can suggest small pale bonnets such as Mycena filopes, but those are grey-brown from the outset and never show a pink or coral phase.