fen

A wetland fed by groundwater or surface water rather than by rainfall alone — distinguished from a bog by its higher nutrient content, its less acidic soil, and its richer plant community. Fens support sedges, reeds, grasses, and wildflowers that bogs cannot. Many fens develop on top of peat, and over time, as sphagnum moss colonizes them and acidifies the water, they can transition into bogs. The Fens of eastern England — once vast, now largely drained for agriculture — are the type example.