Mushrooms are a type of fungus. There are lots of different kinds of mushrooms and some of them are poisonous. Therefore it is not advisable to pick or eat a wild mushroom. The most popular varieties are: Button, Cup and Flat are the same ones. Button is the youngest, Flat is the most open. Portobello is ideal to grill. Chestnut mushroom is the younger version of Portobello. It can be kept in the fridge for 3 or 4 days.