The fruiting body is the actual mushroom cap and stem. Mycelium is the basis method of the mushroom grown on top of a grain substrate causing a supplement that's about 50% roots, 50% filler, and 0% of genuine mushroom. Why would some manufacturers do this? Because mycelium is less costly https://milomykaf.blogdal.com/32859659/5-essential-elements-for-cordyceps-mushroom