CRCritically Endangered

Elm Leech

Hypsizygus ulmarius

Unknown

Photo: Wikimedia Commons (CC) via https://en.wikipedia.org/wiki/Hypsizygus_ulmarius

Overview

Hypsizygus ulmarius, also known as the elm oyster mushroom, and less commonly as the elm leech. It has often been confused with oyster mushrooms in the Pleurotus genus but can be differentiated easily as the gills are either not decurrent or not deeply decurrent.

The Elm Oyster mushroom (Hypsizygus ulmarius) faces severe decline primarily due to the widespread loss of its host trees, particularly elm species, which have been devastated by Dutch elm disease across much of its range. Habitat fragmentation and the removal of dead and dying trees for disease management have further reduced available substrate for this saprobic fungus. Climate change may also be altering the environmental conditions necessary for successful fruiting and spore dispersal.
Threat summary

Habitat

H. ulmarius cultured on hay-infused agar (left) and potato dextrose agar (right) after five days of growth at room temperature

The H. ulmarius mushroom commonly grows on tree species like elm, box elder (Acer negundo), and beech, though it may be found on other trees as well. The fungus accomplishes this by using a complex suite of enzymes that dissolve both cellulose and lignin like laccase. It...

TERRESTRIAL· major

Other threatened species in Lyophyllaceae

Obscure Domecap

Calocybe obscurissima

Unknown

Frequently asked questions

Why is Elm Leech classified as Critically Endangered?

Elm Leech is classified as Critically Endangered — facing an extremely high risk of extinction in the wild — because population sizes are very small, declining sharply, or restricted to a tiny range. The Elm Oyster mushroom (Hypsizygus ulmarius) faces severe decline primarily due to the widespread loss of its host trees, particularly elm species, which have been devastated by Dutch elm disease across much of its range. Habitat fragmentation and the removal of dead and dying trees for disease management have further reduced available substrate for this saprobic fungus. Climate change may also be altering the environmental conditions necessary for successful fruiting and spore dispersal.

Where does Elm Leech live?

Elm Leech occurs in across multiple regions. Country-level distribution data is sourced from the IUCN Red List and cross-referenced with GBIF occurrences.

What are the main threats to Elm Leech?

The main threats to Elm Leech are ai-1, ai-2, ai-3, and ai-4. The full IUCN-classified threat record for this species is detailed on the species page.

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