The fungus Ganoderma sessile, also known as Sessile Ganoderma or Hemlock Varnish Shelf, is a species of polypore in the family Ganodermataceae. Historically, this North American fungus was grouped under the widely known “Reishi” name, Ganoderma lucidum, but recent research has clarified its distinct identity. Like other members of the genus, G. sessile grows on wood and has a characteristic lacquered or varnished appearance. While the mushroom is considered non-toxic, it is functionally inedible as a food source.
Identifying Ganoderma Sessile
The name sessile is derived from the fungus’s physical structure, indicating that its fruiting body typically lacks a distinct stalk or stipe, attaching directly to its host substrate. Ganoderma sessile appears as an annual, shelf-like or fan-shaped bracket that can grow between 3 and 20 centimeters in diameter. Its upper surface is laccate, meaning it has a shiny, varnished appearance, and is often a deep reddish-brown color, sometimes with a bright white margin when actively growing.
The underside of the mushroom features a porous surface, or hymenium, which starts bright white and will quickly bruise a brownish color when touched or scratched. The fungus is common across Eastern North America, found east of the Rocky Mountains, where it grows as a saprobe or weak parasite on dead or declining hardwood trees. It has a broad host range, frequently colonizing the roots and lower trunks of oaks, maples, and beech trees.
Accurate field identification is important because G. sessile can be confused with other local Ganoderma species, such as Ganoderma curtisii, which usually presents with a more developed stem. However, both species can exhibit highly variable growth habits, making the stem unreliable for definitive identification. More reliable distinctions involve microscopic features like spore size and the presence of concentric growth zones in the mushroom’s flesh.
Why It Is Not Eaten
While Ganoderma sessile poses no toxicity risk, it is excluded from culinary use due to its physical properties and taste profile. There are no poisonous look-alikes within the Ganoderma genus, and this species is considered non-toxic. The issue is one of palatability and texture, making it functionally inedible as a traditional food.
The fruiting body of the Sessile Ganoderma is tough and leathery, quickly developing a woody, cork-like consistency as it matures. Unlike mushrooms with a soft, digestible texture, G. sessile is extremely difficult to chew and impossible to digest in its raw or lightly cooked state. This tough texture persists even in younger specimens, preventing its use in traditional cooking methods like sautéing or frying.
The taste further discourages consumption, as the fungus contains high concentrations of compounds that impart a distinctly bitter flavor. These bitter components are considered undesirable in a meal and cannot be easily cooked out or masked by seasoning. Preparation efforts to make it consumable usually involve grinding the dried fungus into a powder or boiling it for an extended period to create a concentrated liquid extract.
Since the cellular structure of Ganoderma species contains chitin, the human body cannot easily break it down. Consuming the whole mushroom does not allow access to the beneficial compounds within. Therefore, the mushroom is rarely consumed as a whole food, but is processed to extract its internal components.
Potential Non-Culinary Applications
Despite its unsuitable texture and taste, Ganoderma sessile is sought after for its non-culinary potential. This aligns with the reputation of other Ganoderma species, which have long been used in traditional East Asian medicine. The mushroom contains a range of bioactive compounds, primarily triterpenoids and polysaccharides, which are the focus of modern research into its supplemental properties.
Specifically, polysaccharides, which include various beta-glucans, are studied for their potential to modulate the immune system and provide antioxidant effects. Triterpenoids are investigated for their anti-inflammatory properties. The dried mushroom is typically processed by chopping or grinding it for use in decoctions, which are long-simmered preparations designed to draw the compounds out of the tough fungal matrix.
Preliminary laboratory studies suggest that G. sessile may be an efficient source of these beneficial compounds. Research indicates that G. sessile is a fast polysaccharide producer compared to other commercially relevant Ganoderma species, achieving high yields in cultivation settings. This makes the species a promising candidate for the manufacture of dietary supplements, but these applications require further clinical investigation.