The oyster mushroom Pleurotus ostreatus is one of the most easily cultivated mushrooms in the world. It is renowned for both its wide range of substrate compatibility and its mild, nutty, oyster-like flavor when cooked. This fungus has also been reported to have a wide array of non-edible uses from mycoremediation to medical applications. Fruiting bodies are fairly large (up to 20 cm), fleshy shelf-like mushrooms of colors ranging from white to gray or brown, and occasionally have yellow, pink, or blue tones. They can be found growing either as individuals or gregarious clusters (Stamets 2005). Sporophytes can be difficult to distinguish from two other species of the genus Pleurotus: P. pulmonarius and P. populinus (Petersen et al. 2014)
P. ostreatus is a widespread white-rot fungus throughout the Americas, Europe, Asia, Northern Africa, and Australia (Mata 1999). It is mainly saprophytic, but can be a facultative parasite on a stressed host. Sporophytes can be found growing naturally on both living and dead trees of a wide array of broadleaf hardwoods and conifers. Many different subspecies, varieties, and strains can be found within this species, but there are two major ecotypes: brown forms from North America and blue/brown forms from Europe (Stamets 2005).
Many varieties can be found throughout most of the hardwood and fir forests worldwide. Sporocarps grow mainly in the spring in the temperate zone, but often grow in the fall in western North America. They thrive in temperatures between 40 and 75 degrees Fahrenheit (Stamets 2005). In the tropics, fruiting can occur year-round in favorable moisture conditions (Mata 1999).
Many varieties can be found throughout most of the hardwood and fir forests worldwide. Sporocarps grow mainly in the spring in the temperate zone, but often grow in the fall in western North America. They thrive in temperatures between 40 and 75 degrees Fahrenheit (Stamets 2005). In the tropics, fruiting can occur year-round in favorable moisture conditions (Mata 1999).
P. ostreatus is characterized by a 4-20 cm cap of oyster or fan shape. Caps range from convex to plane or funnel shaped and has a smooth surface. Color is variable, usually white or gray but can be grayish-brown, tan, or dark brown, and may turn a yellowish hue in old age. Blue and pink sporocarps can be found as well, but are less common. Flesh is thick, white, and soft, becoming thicker near the stipe. Stalk may be absent, but if present is usually 0.5-4 cm long and thick, stout, and off-center or lateral, is solid, dry and usually hairy or downy at the base. Lamellae are broad and decurrent (when a stalk is present), white or grayish in color but range to yellowish in old age. No veil is present. Spore prints are white to pale lilac or lilac-gray. Spores are oblong or elliptical, smooth, and 7-9 x 3-4 microns in dimension (Arora 1979).
Found mostly on hardwood logs and stumps, and occasionally on conifers, P. ostreatus can be found on both living and dead hosts. Though mostly saprophytic, it can become a parasite upon a stressed host. Preferred hosts include cottonwood, oak, alder, maple, aspen, ash, beech, birch, elm, willow, poplar, and sycamore. Colonies may also be found on other decomposing material such as hay bales or discarded coffee grounds. Colonies of fruiting bodies are rarely singular, and are more commonly found in shelving masses and gregarious clusters. A single infected host can be capable of producing hundreds of pounds of mushroom biomass. Mushrooms form in temperatures between 40 and 75 degrees Fahrenheit (Arora 1979, Stamets 2005). P ostreatus often forms a symbiosis with the Gram-negative soil bacteria Bradyrhizobium, in which it trades carbohydrates for atmospheric nitrogen fixed by the bacteria (Jayasinghearachchi 2004).
Plants/saprophyte or parasite:
Quercus – oak
Alnus – alder
Acer – maple, sycamore
Populus – aspen, cottonwood, poplar
Fraxinus – ash
Fagus – beech
Betula – birch
Ulmus – elm
Salix – willow
Bacteria/nitrogen fixing symbiont
Bradyrhizobium
P. ostreatus was first described in 1774 in Austria by Nikolaus Joseph von Jacquin. Originally placed in the genus Agaricus, it was transferred to the genus Pleurotus in 1871. Fruiting bodies are very similar to many other species within the genus Pleurotus, notably P. pulmonarius and P. sapidus. Mating compatibility tests between P. ostreauts and these other species have been able to establish which morphological variants can be accurately placed in this species (Petersen et al. 2014).
Edibility:
P. ostreatus is both edible and delicious. Its taste can be described as mild or nutty, with hints of seafood or an oyster-like taste when cooked. It is commercially cultivated across the world. Nutritionally, these mushrooms are a good source of protein, potassium, fiber and carbohydrates. Additionally they contain low levels of many vitamins and minerals such as calcium, niacin, sodium, and vitamins B5 and D (Stamets 2005).
Medicinal:
P. ostreatus has many potential medicinal uses. It naturally produces isomers of lovastatin, which are well-documented blood cholesterol reducing compounds (Chen et al. 2012). Ubiquitin proteins have also been identified in these mushrooms that have antiviral, and even anti-HIV properties. Studies conducted on rats have also shown oyster mushroom rich diets to inhibit tumor growth and protect from chemicals that induce colon cancer. Though very few people are allergic to these mushrooms when cooked, an estimated 10% of Americans and Europeans may be allergic to raw extracts (Stamets 2005).
Mycoremediation:
One of the most attractive features of this fungus is its adaptability to a wide range of substrate material. Compatible substrates include, but are not limited to: living trees, dead logs, paper, straw, wood, seeds, and coffee grounds. Even toxic compounds often fail to inhibit growth of these persistent fungi. P. ostreatus has demonstrated an ability to break down the core molecular components of oil (Pozdnyakova et al. 2008), creosote (Polcaro et al. 2008), pesticides (Karas et al. 2011, Purnomo et al. 2010), herbicides (Balesteros et al. 2014), waste from munitions production (Axtell et al. 2000), and other industrial toxins such as olive mill wastewater (Olivieri et al. 2006). It has also been shown to be both tolerant of high levels of heavy metal, and able to extract and concentrate these from its substrate (Javaid et al. 2011, Stamets 2005).
Guidance for identification (German text)
Pleurotus ostreatus, the oyster mushroom, oyster fungus, hiratake, or pearl oyster mushroom is a common edible mushroom.[2] 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 2–30 centimetres (3⁄4–11+3⁄4 inches);[3] 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).[4]
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.[5]
Oyster mushrooms on a tree
Details of the gill structure
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As presented in a Korean grocery store
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.[6]
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.[2] 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.[2] The reference to oyster may also derive from the slippery texture of the mushroom.[2] The name grey oyster mushroom may be used for P. ostreatus.[7]
The oyster mushroom is widespread in many temperate and subtropical forests throughout the world, although it is absent from the Pacific Northwest of North America, being replaced by P. pulmonarius and P. populinus.[8] It is a saprotroph that acts as a primary decomposer of wood, especially deciduous trees, and beech trees in particular.[9] It is a white-rot wood-decay fungus.
The standard oyster mushroom can grow in many places, but some other related species, such as the branched oyster mushroom, grow only on trees. They may be found all year round in the UK.
While this mushroom is often seen growing on dying hardwood trees, it only appears to be acting saprophytically, rather than parasitically. As the tree dies of other causes, P. ostreatus grows on the rapidly increasing mass of dead and dying wood. They actually benefit the forest by decomposing the dead wood, returning vital elements and minerals to the ecosystem in a form usable to other plants and organisms.[2] Oyster mushrooms bioaccumulate lithium.[10]
The oyster mushroom is one of the few known carnivorous fungi. Its mycelia can kill and digest nematodes, which is believed to be a way in which the mushroom obtains nitrogen.
The mushroom was first cultivated in Germany as a subsistence measure during World War I[11] and is now grown commercially around the world for food.
The oyster mushroom is a choice edible,[3] and is a delicacy in Japanese, Korean and Chinese cuisine. It is frequently served on its own, in soups, stuffed, or in stir-fry recipes with soy sauce. Oyster mushrooms may be used in sauces, such as oyster sauce. The mushroom's taste has been described as mild with a slight odor similar to anise. Oyster mushrooms are used in the Czech and Slovak contemporary cuisine in soups and stews in a similar fashion to meat.[12] The oyster mushroom is best when picked young; as the mushroom ages, the flesh becomes tough and the flavor becomes acrid and unpleasant.[13]
Some toxic Lentinellus species are similar in appearance, but have gills with jagged edges and finely haired caps.[14]
The pearl oyster mushroom is also used to create mycelium bricks, mycelium furniture, and leather-like products.
Oyster mushrooms can also be used industrially for mycoremediation purposes. Oyster mushrooms were used to treat soil that had been polluted with diesel oil. The mushroom was able to convert 95% of the oil into non-toxic compounds. [15] P. ostreatus is also capable of growing upon and degrading oxo-biodegradable plastic bags;[16] it can also contribute to the degradation of green polyethylene.[17]
{{cite book}}: CS1 maint: uses authors parameter (link) 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.
