Hypsizygus ulmarius

Scientific name:  Hypsizygus ulmarius (Bull.:Fr.) Redhead
Derivation of name:  Hypsi means "high" or "on high" and
zygus means a "yoke" Hypsizygus, then, referring to position
of this mushroom often high in the tree. Ulm- refers to "elm"
indicating one of the common substrates for this fungus.
Synonyms:  Pleurotus ulmarius (Fr.) P. Kumm. and
incorrectly Hypsizygus tessulatus (Bulliard:Fries) Singer
Common name(s):  Elm oyster
Phylum:   Basidiomycota
Order:   Agaricales
Family:   Lyophyllaceae
Occurrence on wood substrate:  Saprobic/parasitic?;
solitary or in small clusters on living hardwoods, particularly
elm (Ulmus) and boxelder (Acer negundo); August through
December. Bessette reports it is ubiquitous on wounds of
living box elders. Miller reports it is often high up in the tree.  
Dimensions:  Caps 5-15 cm wide; stipes 5-10 cm long and
1-2.5 cm thick.   
Cap:  White to buff or tan; sometimes developing a pattern of
cracks with age.       
Gills: Attached but not decurrent; whitish, becoming cream.
Spore print: White to buff
Stipe: Whitish; dry; smooth to finely hairy; stout; off-center to
nearly central.
Veil: Absent.
Edibility: Edible.
Comments: The taxonomy of this species has been quite
confused with a number of field guides and web sites
erroneously recording this species as H. tessellatus. Redhead
(1986) clarifies the nomenclatural history and distinguishes
between H. tessellatus and H. ulmarius primarily on spore
size and secondarily on habit and host. H. ulmarius fruit-
bodies often occur singly as reported by Redhead but may
grow in small clusters as observed in the figures on this page.
H. tessellatus is described as often growing in dense clusters.
Boxelder is a very common host for H. ulmarius but not H.
tessellatus. H. tessellatus often has a pattern of round spots
on the cap surface whereas H. ulmarius does not although it
may develop cracks with age. H. tessellatus is grown in Asia
and marketed in this country as the "Beech Mushroom" or as
hon-shimeji (see photograph).

More information at MushroomExpert.com:
More information at MushroomExpert.com:   
More information at RogersMushrooms.com:

Figure 1. Hypsizygus ulmarius growing from wounds on
a living (although strongly leaning) boxelder. In addition to
the cluster, there is a single specimen closer to the base of
the tree. Photo © Gary Emberger.

Figure 2. A single fruitbody (see Figure 1) growing from a
branch scar site. Photo © Gary Emberger.

Figure 3. A cluster (see Figure 1) of elm oyster specimens
growing from a branch scar site. Photo © Gary Emberger.

Figure 4. Cap surface view of the cluster shown in Figure 3.
Photo © Gary Emberger.

Figure 5. Close up of cap surface of Hypsizygus ulmarius.
Photo © Gary Emberger.

Figure 6. Stipes are nearly central to off-center.
Photo © Gary Emberger.

Figure 7. Gills are attached. Photo © Gary Emberger.

Figure 8. Fruitbodies of this species do not decay rapidly.
Figures 1-6 were taken on September 19. This picture
(and Figure 9) of the cluster of elm oysters shown in
Figure 3 was taken on October 7. Photo © Gary Emberger.

Figure 9. The underside of the specimens shown in Figure 8.
Photo © Gary Emberger.

Figure 10. On October 7, the cluster of mushrooms was
removed revealing the branch scar from which they grew.
Photo © Gary Emberger.

Figure 11. A different cluster of Hypsizygus ulmarius on
the trunk of a tree. Photo © William Roody.


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This page © 2008 by Gary Emberger, Messiah College