It tells you which part of the mushroom is in the jar, and it is one of the few specs on a mushroom supplement that can actually be verified.
Fruiting body
The mushroom itself — the part you would recognise as a mushroom. It is what has traditionally been used and what most of the research uses.
Mycelium on grain
Mycelium is the root-like network the mushroom grows from. It is commonly cultivated on grain, and the usual industrial practice is to harvest and mill the whole thing — mycelium plus the grain it grew on. That grain ends up in the powder, and it is why a "mushroom extract" can contain a substantial proportion of starch.
This is legal and disclosed, in the sense that the label says "mycelium". It just is not obvious what that implies unless somebody explains it.
The number that settles it
Look for a stated beta-glucan percentage. Beta-glucans are the compounds most associated with the mushroom's activity, and a percentage can be checked against a certificate of analysis for that lot.
If a label states only "polysaccharides", that is a broader category that includes starch — so a grain-heavy product can post a high polysaccharide number and look impressive. A stated beta-glucan percentage cannot be inflated the same way.
So: fruiting body, and a beta-glucan percentage. If a label gives you both, it is telling you what you bought. If it gives you neither, that is information too.
Where we stand
Weal Focus prints both: 100% fruiting body, standardised to at least 25% beta-glucans, at 400 mg. That is the least a label can do, not the most.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
Sources for every figure, with the population studied in each, are on our citations page.