A fen is a type of wet meadow fed by an alkaline water source such as a calcareous spring or seep. The deposition of calcium and magnesium in the soil results in an elevated soil pH, and gives rise to a variety of unique plants adapted to surviving these conditions.

Fens are most commonly found in the northeast corner of the state, and in isolated areas along the Illinois River valley.  The vegetation is normally comprised of herbaceous emergents, although woody shrubs or even trees sometimes occur.As is the case with bogs, no specific classification code exists for fens, so the wetland maps cannot be used to pinpoint their location.  In general, they will most often be listed as an emergent wetland.

The soils in this community consist of calcareous silts, clay, and organic materials.  The major soils include Calco silty clay loam, Mound prairie silty clay loam, and Lena muck.


*Used throughout the community descriptions to indicate the most commonly occurring code in Illinois