9 October finds me home again in Bishops Mills, viewing three perfect Elm Knothole Mushrooms growing at head height from a knothole in a tree behind our barn.
These are Hypsizygus ulmarius, the Oyster Mushroom that Fred and I call "Manitoba Maple Knothole Mushroom," though the formal name is "Elm Oyster." Each October we're constantly scanning distant Manitoba Maples for the telltale white spots, often quite high on trunks and branches.
Right now the dehydrator is whirring away in the back porch, drying this year's crop. We slice them and dry them until crisp, then store them in jars in the pantry. Cooked when freshly picked these mushrooms, though very flavourful, are tough and rubbery, but the dried ones cook up nice and tender, and they're a nice snack when eaten dry.
This species lives for most of the year as hidden thread-like mycelia in the quickly rotting wood of most of the Manitoba Maples in eastern Ontario. About Thanksgiving time fruiting bodies slowly blossom from scattered knotholes: whitish caps with pale tan gills, held up on stout curved white stalks. Their flesh is firm and dry, not easily damaged by autumn frosts. This delicious and safely-edible wild mushroom is easy to identify, as no other gilled, stalked, white fungus grows on Manitoba Maples at this season in our area.
Hypsizygus ulmarius is widely cultivated for food under the Japanese name ‘Shirotamagitake.’ The name 'ulmarius,’ suggests growth on Elms, but the only one we’ve seen on an Elm was on a tree drowned by Beaver-flooding, so they don’t seem to use Elms afflicted by Dutch Elm disease, which is how most of our Elms die.