Identifying NZ Oyster Mushroom (Pleurotus purpureo-olivaceus)

Take great care when identifying wild plants and fungi, this blog is not a resource to be taken by itself and further resources will be linked. Consult other sources and double check. While foraging is an extremely rewarding and useful skill, numerous common plants and fungi can make you sick or kill you. Be absolutely sure of what you’re eating and, when gathering, ensure you leave enough not only to ensure the survival and growth of the species but also enough for others to enjoy, from the human and more-than-human communities. Also cultivate an awareness of contamination and pollution – wastewater runoff, spraying, exhaust fumes – as this should affect your decision to harvest.

The Mushroom

Pleurotus purpureo-olivaceus is an indigenous edible species of oyster mushroom (Pleurotus genus) found in Aotearoa, New Zealand. Pleurotus translates to “side ear” as a reference to the distinctive shape of the fruiting bodies. This genus of fungi are saprophytic, consuming decaying organic matter for nutrients.

The gills of P. purpurea-olivaceus, visibly running down the stipe.

Description

This species has a dark grey to brownish-grey cap, paler grey gills, and a white stipe (stem). The stipe grows far to one side of the mushroom. The larger mushrooms will typically be a little smaller than palm size, averaging about 60mm long by 70mm wide, an ideal size for harvesting. The gills are decurrent, meaning they run onto the stipe, and produce a white spore print. The texture is smooth, not slimy or gelatinous, and the mushroom has a tear-able, slightly rubbery consistency. The young mushrooms are flatter with a petal shape, and as they mature will broaden, becoming more ovate in shape. Older mushrooms may have a more ragged edge. These mushrooms typically grow as individuals spreading en masse over their substrate, but sometimes emerge in satisfying clusters similar to cultivated oyster mushroom varieties.

Cross-section of a medium-sized fruiting body.

Ecology

P. purpureo-olivaceus grows exclusively on southern beech trees (Nothofagus family), several species of broad-leafed evergreen natives. We have found them mostly on the fallen trunks and limbs of black beech, Fuscospora solandri, a canopy tree common in lowland, dry areas. This is a good way to ensure you’re getting the right species – if it’s not growing from beech wood, it’s a different mushroom. Season-wise, the fungus is typically fruiting Autumn through Winter.

Nutritional/Medicinal Information

Most Pleurotus species contain good amounts of vitamin B3 (needed for brain function, energy, and cardiovascular health) and vitamin B5 (needed for proper digestion and health skin). They also contain many antioxidants which may help reduce inflammation and oxidative damage to LDL cholesterol and damage to arterial cells, potentially reducing the risk of developing atherosclerosis. The fibre in these mushrooms may help to regulate blood sugar and blood cholesterol levels which in turn may reduce the likelihood of cardiovascular disease, diabetes, and cancers developing.

Possible Lookalikes

Aside from other wild Pleurotus species, the closest lookalike to be aware of in Aotearoa is the shoehorn oyster, Hohenbuehelia petaloides. This species can be often be distinguished by a gelatinous layer in their cap below the cuticle (see above for how P. purpureo-olivaceus should look in cross section), and generally do not grow directly from decomposing wood. With that said, H. petaloides is also apparently edible. Some members of the genus Crepidotus also have a superficial resemblance to Pleurotus species.

Interesting Facts

Some Pleurotus species have been used for myco-remediation of environmental pollutants such as petroleum and hydro-carbons found in coal and oil deposits.

Oyster mushrooms are carnivorous. In order to get the nitrogen they need, they paralyse and consume nematodes (tiny worms) in the soil.

Storing & Cooking

You can dry oyster mushrooms in a dehydrator or oven. Lay out a single layer of mushrooms on a baking tray, fan bake at 70 degrees Celsius with the oven door slightly ajar until dry and crispy. This will take a few hours. Store in a dry, air-tight jar whole or blend into a mushroom powder. To rehydrate just cover mushrooms with boiling water and allow to absorb for 20-30 minutes.

P. purpureo-olivaceus is a delicious alternative to any store brought mushroom and is wonderful in stirfries, soups, pies, pasties, tacos, burgers! Enjoy my fellow foragers!

Further Reading

Hidden Forest

iNaturalist