My recent guest contribution to HerbalGram (American Botanical Council), "Commercial Labeling of Medicinal Mushroom Products”, reveals how U.S. myceliated grain products are being sold as “mushroom”. These grainy products are not mushrooms, but actually a food product called Tempeh, yet they are being sold as mushroom supplements.
"Commercial Labeling of Medicinal Mushroom Products" is a very good primer into differences in mushroom products that are being sold in the marketplace.