Hypsizygus ulmarius

Hypsizygus ulmarius, commonly called the elm oyster mushroom or white elm mushroom, is a saprophytic, brown-rot fungus that fruits on living and dead hardwoods, particularly elms, cottonwoods, beech, maple, and willow. Although its broad cap superficially resembles a true oyster mushroom, it is not closely related to Pleurotus; unique microscopic features and a brown-rot habit place it in the genus Hypsizygus. It is valued as a choice edible and is cultivated commercially, especially in Japan.

History

The taxonomy of this species has a long and confused history. It was originally described from Europe in the Bulliard: Fries tradition and was at various times treated as Pleurotus ulmarius (Bull.: Fr.) Kummer and Lyophyllum ulmarium (Bull.: Fr.) Kühner before Redhead transferred it to Hypsizygus ulmarius in 1984. The genus name comes from the Greek hypsi ("on high" or "aloft") and zygos ("yoke"), while the epithet ulmarius derives from the Latin ulmus, "elm," reflecting its frequent association with elm trees. In Japan it is known as shirotamogitake ("white elm mushroom") and tamo-motashi.

Overview

Ecologically, H. ulmarius is a brown-rot decomposer of hardwoods, in contrast to the white rot produced by Pleurotus ostreatus — a key feature distinguishing the two. The cap is hemispheric to plane (occasionally umbilicate), uniformly tan, beige, grayish brown to gray, 4-15 cm across, with an inrolled-to-incurved margin when young; the gills are decurrent and close, and the stem is thick, eccentrically attached, and curved at the base. Cultivated in Japan since 1973 on hardwood sawdust or logs, it is prized for a firm texture and mild, pleasant flavor. Reported medicinal interest (antitumor/immune-modulating properties) rests largely on anecdotal and unpublished reports and on data from close relatives, so such claims should be treated as preliminary.