When cooking mushrooms, always be sure that you cook them with low heat and do not allow them to cook too long. If you do, they will become tough and will shrivel. Very little liquid is needed in any recipe in which you use mushrooms, because they themselves are ninety percent water.
I saw a book one time that read all mushrooms are edible if prepared properly...w/ a warning to follow the directions if you don't want to become very ill...or even die if not prepared the right way.