Edible
Oyster Mushroom
Pleurotus ostreatus
Oyster mushrooms grow in overlapping shelves with little or no stem, and their gills run down to the point of attachment.
Elm Oyster
Hypsizygus ulmarius
Edible
Also called elm leech.
The elm oyster is a large, whitish to buff mushroom that grows from wounds on elms, box elders and other hardwoods, often high on the trunk, in fall. It resembles an oyster mushroom but has a real stem and gills that do not run down it.
Hypsizygus ulmarius
Photo coming
The tell
Large whitish cap with a distinct stem and gills that attach to it without running down.
Field marks
What to look at
Cap, underside and stem show in a photo. The spore print does not, and it is often the deciding check.
- Cap
- Convex to flat, white to buff or pale tan, without watery spots, sometimes developing a pattern of cracks with age. The edge is inrolled when young.
- Underside
- True gills, white to buff, attached to the stem and usually notched where they meet it, not running down it.
- Stem
- Thick, often off-center or curved, white to buff. No ring.
- Flesh
- White and firm. Smell is mild.
- Spore print
- White to buff.
- Size
- Cap 2 to 6 inches wide (5 to 15 cm); stem 2 to 4 inches long (5 to 10 cm).
Where and when
Where and when it grows
- Habitat
- Hardwood forests, river bottoms, parks and city streets.
- Grows on
- Wounds and dead wood on living or dead hardwoods, especially elm and box elder.
- Season
- Late summer to fall.
- Range
- Widespread in North America, most often reported in the East and Midwest.
Lookalikes
What the elm oyster gets confused with
Each card says how to tell the two apart.
Veiled oyster (Pleurotus dryinus)
Has a cottony partial veil when young that leaves fragments on the cap edge, and its gills run down the stem.
Edibility
What the field guides say
Edible
Field guides list the elm oyster as edible. A close relative, Hypsizygus tessulatus, is cultivated and sold as shimeji or beech mushroom.
This page states what field guides record. It is not advice to eat, taste or handle anything, and a photo cannot settle edibility. If someone has eaten a wild mushroom that may be toxic, call poison control (1-800-222-1222 in the US) right away, before symptoms start: the deadliest species act hours later.
FAQ
Questions about the elm oyster
Is an elm oyster the same as an oyster mushroom?
No. The elm oyster, Hypsizygus ulmarius, is in a different family from the true oyster mushrooms in the genus Pleurotus. It has a distinct stem and gills that attach to it without running down, while oyster mushrooms have little or no stem and gills that run down.
Is elm oyster edible?
Field guides list it as edible. It is firmer than the true oyster mushroom, and a close relative is cultivated and sold as shimeji.
Where do elm oysters grow?
On wounds and dead wood of living or dead hardwoods, especially elm and box elder, often high on the trunk. They fruit from late summer into fall in forests, river bottoms, parks and on street trees.
Sources
Where these facts come from
- Hypsizygus tessulatus
MushroomExpert.com
- Hypsizygus ulmarius
Fungi Growing on Wood, Gary Emberger (MushroomExpert.com)
- Hypsizygus ulmarius
Index Fungorum
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