Flat Crep

Flat Crep (Crepidotus applanatus) is one of the commoner members of a genus of small, stalkless, fan- or shell-shaped gilled fungi that grow attached sideways to dead wood. Fresh caps are white to pale cream and look like miniature oyster mushrooms, but the gills darken to cinnamon or clay-brown as the spores ripen, and the spore print is brown rather than white.

The genus Crepidotus is unified by that brown spore deposit, the lateral or absent stipe, and the habit of fruiting in tiers and overlapping ranks on logs, branches and woody debris. C. applanatus takes its name from its flattened, plane profile — the cap spreads out almost horizontally from its point of attachment, forming a broad, thin fan.

Microscopically the species is distinguished by globose, finely roughened spores, a character that separates it from several similar white creps with ellipsoid spores. In the field, the combination of a smooth non-gelatinous surface, a striate moist margin and a flattened fan shape is usually enough.

Cap

The fruiting body is 1–5 cm across, fan-shaped, kidney-shaped or almost circular where it attaches at one point, flattening out into a broad plane. The surface is white to cream when fresh, becoming pale buff or tan as it dries, smooth and dry to slightly moist but never gelatinous or rubbery. It is hygrophanous: when wet the thin flesh becomes translucent and the margin is conspicuously striate, showing the gills through; on drying the colour pales and the striations fade. A fine white down is often present around the point of attachment.

Gills

The gills radiate outwards from the attachment point, are crowded and narrow, white at first and darkening steadily through pale pinkish-buff to cinnamon or clay-brown as spores mature. The mature gill colour is one of the fastest ways to distinguish a Crepidotus from a white-spored oysterling.

Stipe

There is effectively no stipe. The cap is attached directly to the wood, sometimes by a very short lateral stub or a small white mycelial pad. Fruit bodies frequently overlap in shelving tiers along a log.

Flesh and spore print

The flesh is thin, soft, white and watery, and does not change colour when bruised. The spore print is a pale cinnamon-brown or dull clay-brown. Under a microscope the spores are globose and minutely punctate or roughened, a decisive character for the species.

Flat Crep fruits on dead hardwood: fallen logs, stumps, large branches, and occasionally sawdust and woody debris, most often on wood that has lost its bark and become soft. Beech, maple, oak, birch, alder and poplar are all frequent hosts. Fruit bodies commonly appear in dense overlapping colonies covering a metre or more of a single log.

The season is summer to autumn, extending into mild winters in oceanic climates, and fruiting follows periods of sustained rain. The species is widespread in temperate deciduous and mixed woodland across Europe, North America and Asia, and it is often among the first small gilled fungi noticed on a decaying log in damp weather.

Crepidotus applanatus is a saprotroph producing a white rot in dead hardwood. It typically colonises wood in the middle to later stages of decay, once the bark has fallen and the surface is soft and moisture-retaining, and it thrives in the humid microclimate of the underside and shaded flanks of logs.

The lateral or absent stipe is an adaptation to fruiting on vertical and overhanging surfaces: the cap grows outward and orients its gills downward by adjusting the direction of growth, ensuring spores fall clear. Colonies can be very productive, and the brown spore deposit is often visible dusting the caps of fruit bodies growing immediately below others in a tier.

Peeling Oysterling (Crepidotus mollis) is the most frequent confusion: it is usually larger, has a distinctly gelatinous elastic layer under the cap surface so the flesh stretches noticeably when pulled, and it often shows fine brownish scales near the attachment. Variable Oysterling (Crepidotus variabilis) is much smaller, grows on twigs and small sticks, and has a dry, slightly downy white cap with gills that turn pale pinkish-brown. Crepidotus crocophyllus is separated at once by bright saffron to orange-yellow gills and a scaly, tawny-flecked cap.

White-spored lookalikes include Panellus and small Pleurotus species, whose gills stay white or cream into maturity and which give a white spore print; Panellus stipticus additionally has a tough, tan, felty cap with a short distinct lateral stub. Schizophyllum commune is distinguished by its hairy grey cap and split, folded false gills rather than true blades.