Orange Mycena
Mycena leaiana
Also called lea's mycena, orange bonnet, golden-edged bonnet
A vividly orange, sticky-capped bonnet that grows in dense tufts on hardwood logs and is instantly recognised by the bright orange edges of its otherwise pale gills.
Overview
Orange Mycena is one of the most striking small fungi of eastern North American hardwood forests, forming dense orange clusters on mossy logs that can be spotted from a considerable distance. Where most bonnets are grey, brown or white, this species is a saturated tangerine to apricot orange, and the pigment is generous enough to stain the fingers of anyone who handles it.
The species belongs to Mycena, the vast genus of small, thin-fleshed, white-spored gilled fungi, and is placed among the brightly pigmented, viscid-capped members. Its outstanding diagnostic character is the gill edge: the gill faces are pale cream to pinkish, but each edge is bordered by a narrow band of intense orange, giving the underside of the cap a finely pinstriped appearance.
It is a wood-rotting species, and its bold colouring, sticky cap surface and clustered habit make it one of the few Mycena species that can be named confidently in the field without a microscope.
How to identify it
Cap
The cap is 1–5 cm across, conical to bell-shaped at first and expanding to broadly convex with a low umbo. The surface is bright orange to orange-yellow, often deepest at the centre and fading a little at the rim with age, and is distinctly viscid or sticky when moist — a rare feature among the small bonnets. The margin is faintly striate and may be paler, sometimes cream-orange in older caps.
Gills
The gills are adnate to narrowly attached and moderately crowded. Their faces are whitish, cream or faintly pinkish, but each gill edge is bordered by a sharp band of vivid orange, visible without magnification and unmistakable with a hand lens. In age the faces may pick up dull orange staining from handling or bruising.
Stipe
The stipe is 2–7 cm long and 2–5 mm thick, equal or slightly enlarged below, hollow, tough and slightly viscid, coloured orange to orange-yellow throughout. The base is bound into the wood by a coarse tuft of orange to yellowish hairs, and multiple stipes are typically fused at their bases into a tight cluster.
Flesh and spore print
The flesh is thin and orange-tinged, without a strong odour. Every part of the fruiting body releases orange pigment onto the fingers when rubbed. The spore print is white, confirming placement in Mycena rather than among the rusty-spored wood fungi.
Where and when it grows
Orange Mycena is a hardwood specialist, fruiting on logs, stumps, fallen branches and occasionally standing dead trunks. Beech is a classic host, but maple, birch, oak and other broadleaved trees are used as well. It favours wood at a moderate stage of decay, often mossy, in shaded, humid stream valleys and ravines.
It is primarily an eastern North American species, common from the Great Lakes and southern Canada south through the Appalachians, with records extending west to the Mississippi basin, and related populations reported from eastern Asia. Fruiting occurs from late spring through autumn, with the heaviest flushes in warm, humid summer weather following rain.
Ecological role
The species is a wood-decaying saprotroph, colonising the sapwood of fallen broadleaved trees and contributing to their breakdown. Its mycelium spreads through the outer layers of the log and fruits densely wherever it reaches the surface, which is why colonies appear as discrete orange tufts scattered along the length of a single trunk.
The orange pigment is a group of compounds concentrated in the cap cuticle and gill edges. Pigment-rich gill edges of this kind occur repeatedly across Mycena and are generally interpreted as deterrents to invertebrate grazing on the spore-producing surface, which is the most vulnerable and most valuable tissue in the fruiting body.
Similar species
Mycena acicula is another small orange bonnet, but it is far smaller, has a bright orange cap contrasting with a yellow stipe, grows singly or scattered on twigs and litter, and lacks both the viscid cap and the orange gill edge. Mycena strobilinoides is a red-orange bonnet of western montane conifer duff with orange gill edges, but its cap is dry rather than sticky and it grows in needle litter, not clustered on hardwood logs.
Xeromphalina campanella shares an orange colour and clustered habit but is much smaller, has a dry, centrally depressed cap, distinctly decurrent and cross-veined gills, and a dark brown stipe base. Orange waxcaps in the genus Hygrocybe have thick, waxy, often decurrent gills without a coloured edge and fruit in grassland or moss on soil rather than on wood.