Pleurotus populinus,
and Pleurotus pulmonarius

Pleurotus ostreatus	Pleurotus populinus	Pleurotus pulmonarius

Common name: P. ostreatus: oyster or pearl oyster mushroom, P. populinus: aspen oyster mushroom, P. pulmonarius: phoenix or Indian oyster mushroom.

Description and identifying characteristics:

Pleurotus ostreatus has a white to gray to grayish brown to brown, fan or oyster shaped cap that ranges from 2 to 10 in. (5 to 25 cm.) broad and 1 ½ to 6 in. (3 ¾ to 15 cm.) wide. Cap color is lighter in the spring and darker in the fall. The margin ranges from semicircular to lobed and wavy. When attached as a shelf on trees, there is at most a rudimentary thick stalk and often none. The flesh is quite thick ranging from ½ to 1 ½ in. (1.25 to 2 ¾ cm.) thick. When the oysters grow from the top of a log, there is a thick stalk. The white, close to almost distant gills are decurrent descending the entire stalk.

P. ostreatus has a white to grayish to lilac spore print, and grows in shelf-like clusters on dead logs and living trees. It usually grows with hardwoods, but is occasionally found on conifers. It fruits throughout the year under favorable conditions.

Pleurotus populinus has a white to pinkish buff to orange gray, fan or oyster shaped cap that ranges from 1 ½ to 8 in. (3 ¾ to 20 cm.) broad by 1 ½ to 5 in. ( 3 ¾ to 12.5 cm.) wide. The white to cream colored, close to almost distant gills are slightly decurrent running a small way down the stem. The cap margin becomes finely scalloped with age.

P. populinus has a buff spore print, and grows in shelf-like clusters on aspens and cottonwoods (Genus Populus). It fruits in late spring and throughout the summer.

P. pulmonarius has a pale white, lung-shaped to semicircular (circular when the mushroom grow in top of logs) cap that ranges from ¾ to 4 ½ in. (2 to 12 cm.) broad and ½ to 21/2 in. ( 1 ¼ to 7 cm.) wide. The white, close to nearly distant gills are decurrent if there is a stem. P. pulmonarius has a white to grayish to lilac spore print, and grows in shelf-like clusters on dead and living wood of hardwoods (in the West it has been found on conifers). P. pulmonarius fruits in July and August.

P. populinus can be distinguished form the other two species by its buff spore print. P. ostreatus can is generally larger and more robust than P. pulmonarius, and can be distinguished on that basis.

All three species can occur singly but more commonly they are found fruiting in clusters. Often, many pounds of oyster mushrooms can be collected from a single tree or log. All three species are similar in odor and taste, and have been cooked in the same manner and used in many dishes without any need to distinguish between the species.

Ecology/associated hosts: Pleurotus species are saprotrophic, causing a white-rot of the dead or living wood they are growing on. Oyster mushrooms tend to be found growing on hardwoods but occasionally, especially in the West, they are found with conifers. In addition to being saprotrophic, they are parasitic on nematodes and bacteria they encounter.

Look-alikes: There are no poisonous look-alikes. Because some Japanese consumers who had previously compromised livers died after consuming Pleurocybella porrigens, it is recommended that this look-alike be considered potentially dangerous. Pleurocybella porrigens (shown below) grows on conifers, and has relatively thin flesh whereas all oyster species are thick fleshed.

Hypsizygus tesselatus, the edible elm oyster (shown below), grows singly and has a distinct long stem, and its’ caps crack and turn yellow with age. All Lentinus and Lentinellus species, while shaped like oysters, have jagged gill edges, while oysters have smooth gill edges (one reason why carrying a magnifying loupe is recommended). Crepidotus species are much smaller, are very thin fleshed and have a brown spore print.

Pleurocybella porrigens

Hypsizygus tessulatus

Crepidotus applanatus

Tips on harvesting: Cut oyster mushrooms off of the trees or logs or stumps they are growing on at the point of attachment to the wood. With large specimens, the very thick flesh near the attachment point might be very tough. If the flesh is tough, cut into the oyster further from the attachment points.

Oyster mushrooms can be cleaned with a brush. Occasionally, some tree bark will stick to the top of the cap or to the flesh where cut from the tree. If that happens, cut out the wood with a knife. In late spring and through the summer, one often finds small red and black beetles on the oyster mushrooms, especially in the gills. Brush off the beetles and check the flesh of the mushroom for beetle larvae. If the mushroom only has adult beetles, no problem. If the mushroom is infested with the larvae, it should not be eaten.

When you find a manageable oyster log, you can take it home, keep it outdoors in a location protected from sun and wind, and occasionally water when the weather is dry (soaking is best). Oysters logs can continue to produce for two to four years.

Oyster mushrooms will often quickly consume the wood they’re growing on, so one does not often find oysters for many years on the same tree. They will last for a few years, however, so it is good to remember where you have found them before.

Older specimens will begin to yellow and the margins will become ragged. When this occurs, the oysters are too far gone for consumption.

Possible allergic reactions and symptoms: All of the species of oyster mushrooms are considered edible and choice. There are no records of problems caused by eating oysters. In China and Japan they have been cultivated for centuries and used for the table.

Mushrooms are very prolific organic chemical laboratories. They produce many acids and other chemicals to break down their substrate for nutrition. As a result, people can have allergies to specific mushrooms, so it is wise to consume only a small amount when trying any mushrooms for the first time.

Oysters do produce a huge amount of spores, and reports of allergies to the spores are common in the mushroom cultivation industry. Some allergic reaction from spores have also been reported from those who have gathered a huge cache of oyster mushrooms. Symptoms include itchy eyes, running noses, and rashes.

Other uses: Oyster mushrooms are one of if not the easiest mushrooms to cultivate. In addition to culinary uses, oyster mushrooms have been applied to various organic contaminants to break down the contaminant. Oysters have been used to neutralize petroleum product spills, break down biological warfare agents, and even to break down disposable diapers!

Photos:

Oysters showing decurrent gills	Small clump of oysters
Oysters in a rosette on top of log	Nice clump of oysters
Very crowded oysters	Some old specimens
A nice group of oysters	A huge clump of oysters

References:

Kuo, Michael (February 2005) Pleurotus ostreatus: The Oyster Mushroom

Michigan Mushroom Hunters Club, June 2009 Mushroom of the Month

Volk, Tom Fungus of the Month for October 1998. 

Arora, David (1979, 1986) Mushrooms Demystified, Ten Speed Press, pp. 134-35

Kuo, Michael and Methven Andrew S. (2014) Mushrooms of the Midwest, University of Illinois Press, pp 314-15

Lincoff, Gary H. (1981) National Audubon Society Field Guide to North American Mushrooms, Alfred A. Knopf , pp. 793-94, plates 484, 497.

Phillips, Roger (1991, 2005) Mushrooms and Other Fungi of North America, Firefly Books, p. 206.

Binion, Denise E., Stephenson, Steven L., Roody, William C., Burdsall Jr., Horold H., Vasilyeva, Larissa N., and Miller Jr., and Orson K. (2008), Macrofungi associated with oaks of Eastern North America, West Virginia University Press, pp. 396-97.