Bog relicts are peatlands found in kettle basins in interlobate and end moraine regions in southern Wisconsin that developed under a cooler climate after glaciers retreated. They can also occur in the Driftless Region but are very uncommon in that landscape and limited to a handful of known sites. Unique in southern Wisconsin, bog relicts are underlain by highly calcareous groundwater but contain ombrotrophic areas where Sphagnum peat raises the surface and creates a highly acidic environment. Bog relicts thus tend to be heavily dominated by leatherleaf and occasionally huckleberry with a continuous layer of Sphagnum moss, though large areas of bog or poor fen sedges (i.e., Carex oligosperma, C. lasiocarpa) may also be present. Wiregrass is especially common in wetter zones in contact with more mineral rich groundwater.
Tamarack may be present either on the margins of more open sites or in the interior, but rarely forms a continuous canopy. Tall shrubs include poison sumac and bog birch, though density and cover are variable. Many sites have a narrow moat with more minerotrophic species where groundwater seepage and runoff from uplands meets the wetland edge.
Bog relicts support a number of bog and poor fen species typically found further north, including small cranberry (Vaccinium oxycoccos), large cranberry (Vaccinium macrocarpon), rose pogonia (Pogonia ophioglossoides), tawny cotton-grass (Eriophorum virginicum), bog St. John’s-wort (Triadenum fraseri), and insectivorous plants such as roundleaf sundew (Drosera rotundifolia), spoon-leaf sundew (Drosera intermedia), pitcher plant (Sarracenia purpurea), and intermediate bladderwort (Utricularia intermedia). Many of these bog relict indicators are at or near the southern edge of their range in southern Wisconsin and are evidence of these sites being relicts of a cooler climate in the past.
Acidic wetlands with a floating sedge mat in southern Wisconsin are also included in the bog relict concept. While they have many similarities to poor fen, the latter is widely defined as a northern plant community occurring in a cool climate, whereas sites south of Wisconsin's tension zone are considered climate relicts, and thus, "bog" relicts, despite their similar flora. Soils in bog relicts are deep, saturated Sphagnum peat and are usually very strongly to ultra acidic (pH 3.0–5.0). Mosses are abundant and can form large hummocks comprised of Sphagnum magellanicum (bog moss), members of the Sphagnum recurvum group, and Polytrichum strictum (strict haircap moss). Local poor fen pools can contain Sphagnum cuspidatum (feathery bog moss or drowned kittens).
