Many cuisines use dried mushrooms as ingredients, but this mushroom was intended to be cooked while it was still fresh. It was sliced in preparation for a meal, but these slices got misplaced, and they eventually dehydrated. Mushrooms are believed to boost the immune system, but this one will not have such an opportunity.
White button (also known by other names such as common or champignon), crimini (brown), and portobello are just different states of maturity of the same type of mushroom. These slices were likely from a white button mushroom, but have substantially shrunken, dried, and turned a toasty brown. NEXT >