Pleurotus ostreatus

Pleurotus ostreatus, the oyster mushroom, oyster fungus, hiratake, or pearl oyster mushroom is a common edible mushroom. It is one of the more commonly sought wild mushrooms, though it can also be cultivated on straw and other media. The mushroom has a broad, fan or oyster-shaped cap spanning ; natural specimens range from white to gray or tan to dark-brown; the margin is inrolled when young, and is smooth and often somewhat lobed or wavy. The flesh is white, firm, and varies in thickness due to stipe arrangement. The gills of the mushroom are white to cream, and descend on the stalk if present. If so, the stipe is off-center with a lateral attachment to wood. The spore print of the mushroom is white to lilac-gray, and best viewed on dark background. The mushroom's stipe is often absent. When present, it is short and thick. It has the bittersweet aroma of benzaldehyde (which is also characteristic of bitter almonds). P. ostreatus is a carnivorous fungus, preying on nematodes by using a calcium-dependent toxin that paralyzes the prey within minutes of contact, causing necrosis and formation of a slurry to facilitate ingestion as a protein-rich food source. It is related to the similarly cultivated Pleurotus eryngii (king oyster mushroom). Other similar species include Pleurocybella porrigens, Hohenbuehelia petaloides, and the hairy-capped Phyllotopsis nidulans. Omphalotus nidiformis is a toxic lookalike found in Australia and Japan. In North America, the toxic muscarine-containing Omphalotus olivascens (the western jack-o'-lantern mushroom) and Clitocybe dealbata (the ivory funnel mushroom) both bear a resemblance to P. ostreatus. Both the Latin and common names refer to the shape of the fruiting body. The Latin pleurotus (side-ear) refers to the sideways growth of the stem with respect to the cap, while the Latin ostreatus (and the English common name, oyster) refers to the shape of the cap which resembles the bivalve of the same name. The reference to oyster may also derive from the slippery texture of the mushroom.