ulmarius

Elm Oyster

Hypsizygus ulmarius is a large, saprotrophic gilled mushroom often found growing high on the trunks of hardwood trees, particularly elms and boxelders. Unlike the true oyster mushrooms (Pleurotus species) it resembles, H. ulmarius possesses adnexed or adnate gills rather than deeply decurrent ones, and its stem is typically central or slightly off-center rather than lateral. The cap is convex to broadly convex, ranging from white to cream or pale tan, often developing a cracked or areolate surface with age. This species is distinct from Hypsizygus tessellatus (Buna-shimeji) in its growth habit and morphology. While H. tessellatus typically grows in dense, caespitose clusters and often features watery spots on the cap, H. ulmarius usually fruits singly or in small groups of 2-3 and lacks the characteristic water spots. It is a robust fungus known for its high biological efficiency in cultivation and ability to fruit in cooler temperatures.