A crimini mushroom is actually an immature portabello mushroom, native to the grasslands of Europe and North America. Criminis differ from white mushrooms in that their skins are usually brown. (Read more about mushrooms on Wikipedia.)
Crimini mushrooms are a good source of riboflavin, niacin, pantothenic acid, copper, and selenium-an important antioxidant that may help prevent chronic diseases such as cancer and heart disease. (See more mushroom nutrition facts on Self.com.)
Prepackaged mushrooms can be stored, unopened, in the refrigerator for about one week. Once opened, mushrooms should be moved to a paper bag and refrigerated.