A type of wetland ecosystem characterized by wet, spongy, poorly drained peaty soil. The term also describes the communities of plants growing on acid waterlogged ground, as opposed to fen. Three main types of bog exist: valley bogs that remain waterlogged due to the concentration of drainage into a valley; raised bogs that form as large pillows of peat and are kept waterlogged by high rainfall; and blanket bogs that form through the growth of the organic horizons of gleyed podzols.