Shiitake Identification Guide

The first impression

Shiitake announces itself as a wood fungus before you have looked at a single microscopic character. You find it shelving out of a dead hardwood log, a standing snag or a cut stump, the caps arranged in overlapping tiers or scattered singly along the length of the wood, each one a warm umber to tan dome flecked with paler woolly patches. The build is chunky and firm rather than delicate: the cap is thick-fleshed, the margin stays rolled under for a long time, and the stalk feels like a piece of fibrous rope when you squeeze it. Everything about the fruit body says wood decomposer, and the tough, almost leathery texture of the stalk is one of the first field impressions worth registering.

Reading the cap

The cap is typically 5-12 cm across, sometimes reaching 20 cm on a well-fed log. Young caps are hemispherical, almost spherical in the button, and expand through convex to broadly flat, often with a shallow depression at the centre in age. The surface is dry, never sticky, and finely velvety at first. Colour is a mid to dark brown, umber, chestnut or coffee, characteristically darkest at the centre and lighter toward the rim. As the cap expands, the surface layer breaks up into pale buff to whitish woolly scales and cracks that expose paler flesh beneath, so a mature cap looks brown patterned with cream flecks, sometimes with the cracks arranged in a coarse net. The margin is inrolled when young and frequently hung with soft white fragments of the partial veil, which persist as a ragged fringe long after the veil has torn.

The gills and their edges

Turn the cap over and look closely with a lens, because the gill edge is one of the best characters. The gills are white to cream, crowded, moderately deep, and attached to the stalk with a notch, sometimes with a very short decurrent tooth. Their edges are not smooth: under magnification they are minutely serrate, finely saw-toothed or eroded, a feature that runs right through the wider group this species belongs to. Handle the gills and they bruise slowly to reddish brown, and old fruit bodies develop the same rust-brown staining spontaneously along the gill edges and faces. That combination - crowded white gills, toothed edges, slow brown bruising - is a strong package.

Stalk, veil and base

The stipe is 3-8 cm long and 1-1.5 cm thick, central on caps growing from the top of a log and distinctly off-centre or nearly lateral on caps growing from a vertical face. It is solid, tough and coarsely fibrous, so much so that it twists rather than snaps when you try to break it. Above the veil zone it is whitish and smooth; below it is pale brown and covered in fine fibrils and small recurved scales. The partial veil is cottony rather than membranous, and when it tears it leaves an indistinct fibrillose ring zone on the upper stalk plus the fringe on the cap margin, rather than a clean skirt-like ring. The base is not bulbous and there is no sac, but it usually sits in a mass of white mycelium bonded to the wood.

Flesh and colour change

Section the fruit body vertically. The cap flesh is thick, white and firm, and the stalk flesh is white and markedly tougher, with visible longitudinal fibres. On cutting, the flesh does not flush red, blue or yellow; instead it stains slowly and mildly brownish over minutes to hours, and the same slow browning shows wherever the fruit body has been bruised or insect-damaged. The odour is pleasant and faintly aromatic, sometimes with a hint of the smell of the wood it is growing on, and it is not mealy, garlicky or chemical.

Taking a spore print

Sever the tough stalk with a knife rather than tugging, place a mature cap gills-down on black paper, cover, and wait. Shiitake drops a white spore print, occasionally with the merest cream tint on a heavy deposit. This is important, because several of the brown scaly wood-dwellers that resemble it give rusty brown prints. Microscopically the spores are small, smooth, thin-walled, ellipsoid to cylindric, and inamyloid, typically around 5-6 by 3 micrometres. The gill edge is packed with sterile cells, which is why the edge reads as finely toothed under a lens.

Substrate and season

This is a saprotroph of dead broadleaved wood in the warm-temperate and subtropical forests of East and Southeast Asia, its natural range running through Japan, China, Korea, Taiwan and into the Himalayan foothills and Southeast Asian uplands. Its classic natural substrate is the shii tree and its relatives in the beech family, along with oak, chinquapin, hornbeam, sweetgum and other hardwoods. It fruits on fallen trunks, standing dead stems and stumps, usually after a drop in temperature followed by rain, so the main flushes are in autumn and spring in mild climates and it can appear through winter where frosts are light. It is also grown worldwide on inoculated hardwood logs and compressed sawdust blocks, so a fruit body encountered far outside its native range is far more likely to be associated with cultivation than with wild forest.

Separating the look-alikes on morphology

Neolentinus lepideus shares the scaly cap and toothed gill edges but is a conifer specialist, fruiting on pine and spruce timber, railway sleepers and structural wood. Its cap ground colour is cream to pale ochre with darker appressed scales rather than a brown ground with pale flecks, its ring is more distinct, and its gills are strongly decurrent with coarsely ragged edges.

Pholiota species can match the scaly brown cap, but they are usually viscid in wet weather, grow in dense clustered tufts, and drop a rusty or clay-brown spore print - the single fastest separation.

Armillaria species are also clustered wood-dwellers with a white print, but their cap scales are fine dark tufts on a honey-yellow ground, their ring is a proper cottony collar high on the stalk, and black bootlace rhizomorphs are usually visible in the wood or under the bark.

Panus and Lentinus relatives are tougher still, often funnel-shaped with strongly decurrent gills and hairy or violet-tinged caps.

Pleurotus species are the shelf fungi most often confused at a distance, but they have a lateral or absent stalk, gills running far down what stalk there is, smooth pale caps with no scales, and no veil at all.

Gymnopus and other small wood agarics lack the thick flesh, the veil fringe on the cap margin and the tough fibrous stalk.

Field checklist

On dead hardwood; thick brown cap flecked with pale woolly scales; long-inrolled margin with veil fringe; crowded white gills with finely toothed edges bruising brown; tough fibrous stalk with a fibrillose ring zone; white spore print. Together those characters define Lentinula edodes.