Oyster Mushroom
Pleurotus ostreatus
Oyster Mushroom (Pleurotus ostreatus) grows in overlapping shelves of smooth, fan-shaped caps, pale to dark brown and fading to buff, on living and dead hardwood trees and logs, with whitish gills that run down to a short stub of a stem or to no stem at all. iNaturalist's 5 research-grade Black Hills records are all from Lawrence County, April to July.
Free photos from other sources
| Family | Pleurotaceae · Oyster mushroom |
|---|---|
| Type | Gilled mushroom |
| Season | April into July in Black Hills iNaturalist records; regional records also September and October |
| Size | Cap 3–15 cm (1–6 in) wide; stem short and off-center, or none |
| Grows on | Living and dead hardwood trunks, stumps and logs |
| Spore print | White to pale lilac-gray |
| Also called | čhaŋnákpa ská (Lakota) |
| Toxicity | It has made people sick: cases reported to the North American Mycological Association include cramps, nausea, vomiting and diarrhea, and the association lists the oyster mushroom group among mushrooms that upset the stomach of some people when combined with alcohol. |
| Eating | This guide doesn't say which mushrooms are safe to eat. |
| Note | Kuo gives this species' season as October to early April, and late April to September for the often paler Pleurotus pulmonarius. |
How it lives
A saprobe: it lives on dead wood, which it breaks down into a white rot, and it also fruits on living trees.
How do you identify Oyster Mushroom?
Look for shelves of smooth, kidney- to fan-shaped caps, 3–15 cm (1–6 in) across, often overlapping on a trunk, stump or log. The caps are pale to dark brown, fading to buff; other oysters in the group can be whitish, cream or grayish. The whitish gills run down onto a short, off-center stem, or to the point where the cap joins the wood; on top of a log the stem can be central. The flesh is thick and white, there is no ring, and the spore print is white to pale lilac-gray. The Elm Oyster (Hypsizygus ulmarius) usually grows alone or in twos and threes from wounds in box elder and elm, has a real stem 5–10 cm (2–4 in) long, and its gills attach to the stem without running down it. The Aspen Oyster (Pleurotus populinus), a close relative with 2 research-grade Black Hills records on iNaturalist, grows only on aspen and cottonwood, is never dark brown, and leaves a whitish spore print that is never lilac. Crepidotus species, which also lack a stem and grow attached right to the wood, leave a brown spore print.
When can you find it?
April into July in Black Hills iNaturalist records; regional records also September and October.
Where does it grow?
Living and dead hardwoods: standing trunks, stumps and fallen logs, and sometimes conifers. iNaturalist has 5 research-grade Black Hills records of this species, all from Lawrence County between April and July, plus 2 of the Aspen Oyster and 21 more oyster records still awaiting confirmation, from Lawrence and Pennington counties and Crook County, Wyoming. A 1961 oyster mushroom specimen from the Wyoming side of the Hills, not named to species, is at the New York Botanical Garden, and Sitting Bull College's 1998 Lakota plant book says oyster mushrooms grow on dead deciduous trees through spring and summer.
Other mushrooms to compare
Sources: Kuo, Pleurotus ostreatus (2017) — MushroomExpert.com; Kuo, Pleurotus populinus (2019) — MushroomExpert.com; Emberger, Pleurotus spp. (oyster mushrooms) — Fungi Growing on Wood, archived at MushroomExpert.com; Volk, Pleurotus ostreatus, the Oyster Mushroom: Fungus of the Month, October 1998 — University of Wisconsin-La Crosse; Emberger, Hypsizygus ulmarius (elm oyster) — Fungi Growing on Wood, archived at MushroomExpert.com; Black Elk & Flying By, Culturally Important Plants of the Lakota (Sitting Bull College, 1998), filed with the South Dakota PUC; Species Fungorum: Pleurotus ostreatus — Royal Botanic Gardens, Kew; Mushroom Poisoning Syndromes — North American Mycological Association; Beug, Summary of the Poisoning Reports in the NAMA Case Registry for 2006 through 2017 — North American Mycological Association; iNaturalist: Pleurotus (all species) in the Black Hills places (Black Hills ecoregions, Black Hills National Forest, Wind Cave NP, Custer SP); iNaturalist month histogram, Pleurotus ostreatus, research grade within 500 km of the Black Hills; GBIF occurrence: Pleurotus, Black Hills (Wyoming), 1961 (NY 01933713); Beug, Summary of the Poisoning Reports in the NAMA Mushroom Poisoning Case Registry: 2018 through 2020 — North American Mycological Association.