The acidic, nutrient-poor wetland dominated by sphagnum moss is a bog.
Bogs form where waterlogged conditions slow decomposition, allowing partially decayed plant material to accumulate as peat. Sphagnum moss is especially important because it can hold many times its dry weight in water and releases acids as it grows. Over time, this creates water that is acidic and low in mineral nutrients.
Because bog water is chemically challenging, bogs support specialized plants. These may include sedges, heathers, bog rosemary, cranberries, and carnivorous plants such as sundews and pitcher plants, which supplement limited nutrients by capturing insects.
Bogs are often confused with fens. Both can contain peat and remain wet, but fens usually receive groundwater or mineral-rich runoff, making them less acidic and more nutrient-rich. Marshes are generally dominated by grasses, reeds, or other herbaceous plants, while swamps are typically characterized by woody vegetation such as trees and shrubs.