Mushrooms are another type of floral in Minecraft. In Creative mode, they're simple decorations, while in Survival mode they serve a great role. There are two types, Brown, and Red/White.
Brown Mushroom
Brown Mushrooms, in Survival mode, are very important. Right clicking with them heals two and a half hearts. They cannot be placed in it, either. Pigs drop up to 4 of them upon being killed. Sheep if attacked enough can yield mushrooms too, though one should consider the situation, as sheep also yield cloth blocks if given enough time. These mushrooms are rare, and should be saved until a more dire situation in Survival mode. They may be used as a weapon against mobs. Mushrooms like these also can be found underground, so looking down there can yield a few.
Red and White Mushroom
Red and White Mushrooms are a hazard in Survival mode. To make it worse, you cannot plant these, and they're found much common then Brown ones. Upon eating, you lose one and a half hearts. They can still be used as a weapon, however. These mushrooms are destroyed in sunlight, so you can eliminate the threat of them using this stragety.