Pleurotus ostreatus

(Jacq.) P. Kumm.

Abundant fruiting on a well-decayed poplar stump in Pitsea, Essex.
Numerous fruiting bodies on a willow pollard in Bedford, Bedfordshire.
More jelly-like fruiting bodies on a fallen beech in the New Forest, Hampshire.
Over-mature fruiting bodies on horse chestnut in Greenwich Park, London.
Infrequent darker upper surface and clustered gills beneath on horse chestnut in Hatfield, Essex.

Abundant fruiting on a well-decayed poplar stump in Pitsea, Essex.
Numerous fruiting bodies on a willow pollard in Bedford, Bedfordshire.
More jelly-like fruiting bodies on a fallen beech in the New Forest, Hampshire.
Over-mature fruiting bodies on horse chestnut in Greenwich Park, London.
Infrequent darker upper surface and clustered gills beneath on horse chestnut in Hatfield, Essex.
The gills arrangement emanating from the attachment.
Mature fruit bodies with an upturned rim on chestnut in Billericay, UK.
A closer look at the gills.
A damaged mature fruit body on birch in Rochford, UK.
A bleached fruit body on birch in Hockley, UK.

Common name

Oyster mushroom.

Often found on

Beech, birch, horse chestnut, oak, poplar.

Sometimes found on

Other broad-leaved tree species.

Location

Found across the entire structure of the standing tree and persists on fallen trees.

Description

Annual. Gilled abundantly. Often occurs in clusters. Sometimes with a whitish stem. Variable in appearance. Individually can develop to a fair size. Upper surface may be white, grey (many shades), brown, charcoal black, or blue-black and may or may not be wet. Gills always an off-white. Desiccates to a beige-brown – sometimes tinged – and shrivels. Whitish spore.

Confused with

Pleurotus dryinus (usually larger, singular, and with a silvery felted upper surface).

Significance

Attributed often to a selective white rot of the wood but with the ability to simultaneously degrade lignin and cellulose. Potentially weakly parasitic though often saprobic. Widespread fruiting across the trunk or scaffold limbs can cause concern, as regards structural stability. Can be associated with physiological decline when present alongside fungi such as Chondrostereum purpureum.