Lion's Mane
Hericium erinaceus
Also called bearded tooth, monkey head, pom pom mushroom, hedgehog mushroom
An unmistakable white cushion of long, downward-hanging spines that grows from wounds on standing hardwoods, looking like a frozen waterfall or a shaggy mane.
Overview
Lion's Mane is one of the most instantly recognisable fungi in the world. Instead of a cap and gills it produces a rounded, unbranched cushion of tissue from which hundreds of soft white spines hang straight down, giving a shaggy, icicle-like or fleece-like appearance quite unlike anything else on a tree trunk.
It belongs to Hericium, a small genus of toothed fungi in the Hericiaceae. All members of the genus produce their spores on downward-pointing spines rather than on gills or in pores, an arrangement that has evolved several separate times among fungi. H. erinaceus is the species with a single solid mass and the longest spines; its relatives are branched, with shorter teeth arranged along the branches.
Ageing changes the look considerably. Pure white when young, the fruiting body yellows to cream, then tan and finally brownish, and the spines shrink and clump together, so late-season specimens can look like a discoloured sponge hanging from the bark.
How to identify it
Fruiting body
A single rounded, cushion-like or club-shaped mass 5–40 cm across, attached to the wood by a narrow tough base and hanging outward or downward. It is unbranched — this is the key structural character of the species. Surface colour is white when fresh, ageing through cream and yellow to ochre-tan, and the whole structure is soft and slightly spongy but firmly attached.
Spines
The fertile surface consists of crowded, soft, downward-hanging spines 1–5 cm long, all arising from the underside and outer face of the single mass and all pointing the same way. They are slender, tapering and flexible, drooping like a beard or a set of icicles. Their uniform length and unbranched arrangement distinguish this species from its relatives.
Flesh & spore print
Internally the fruiting body is white, soft and fibrous, with a tougher, denser attachment point where it meets the wood. Cut flesh does not change colour. The spore print is white; spores are roughly spherical, minutely roughened and amyloid.
Where and when it grows
Lion's Mane fruits from wounds, broken limbs, frost cracks and old pruning scars on standing hardwoods, and also on recently fallen logs of the same species. Oak and beech are the classic hosts in Europe, with maple, walnut, sycamore and American beech commonly used in North America; a single wound may produce a fruiting body in the same spot for several consecutive years.
It is widespread but generally uncommon across Europe, temperate Asia and eastern North America, and in parts of its European range it is a protected species associated with old-growth and veteran trees. Fruiting bodies appear from late summer through autumn, often high on the trunk where they are easiest to spot after leaf fall.
Ecological role
Hericium erinaceus is a white-rot fungus that acts as both a wound parasite and a saprophyte. It enters the heartwood of a living hardwood through an injury and slowly degrades lignin and cellulose there, producing a pale, soft, stringy rot, then continues to decay the same wood after the tree dies or the limb falls. Its long residence inside a single tree explains the tendency to fruit repeatedly from exactly the same wound.
Because it depends on large, old, wounded trees, it is treated as an indicator of continuity in mature woodland: it is much more frequent in ancient parkland and old-growth stands than in young managed forest. The hollows it helps create in living trunks contribute to the cavity habitat used by bats, owls and saproxylic beetles.
Similar species
Coral Tooth (Hericium coralloides) is the closest relative and is separated by structure rather than colour: it forms a branched, coral-like framework with short spines, mostly under 1 cm, arranged in rows along the upper and lower sides of the branches, instead of a single unbranched cushion with long hanging spines. Bear's Head Tooth (Hericium americanum) is intermediate, with a branched body but longer clustered spines hanging in tufts from the branch tips.
Tiered Tooth (Hericium cirrhatum) forms overlapping, shelf-like tiers of flattened caps with spines beneath each tier, giving a bracket-like profile that H. erinaceus never shows. Northern Tooth (Climacodon septentrionalis) also grows from wounds on living hardwoods but produces large, tough, tiered brackets with a hairy upper surface and spines only on the underside, and it yellows and browns strongly with age.