Open bogs are distinguished by their strongly acidic peat soils isolated from the influence of mineral-rich groundwater by deep layers of Sphagnum and tall Sphagnum-ericad hummocks. They can be differentiated from poor fens by their lower pH, tall Sphagnum hummocks, a rooting zone isolated from surface and/or groundwater, and relatively low species diversity. Most "bogs" surrounding lakes in northern Wisconsin are better classified as poor fens, especially those with a diverse flora on floating mats. Open bogs may lie adjacent to black spruce swamps and muskegs, also known as treed bogs, but can be differentiated from these communities by typically having less than 10% cover of tree species.
Open bogs share some characteristics with central poor fens, like strongly acidic soils influenced by Sphagnum, but central poor fens lack the strong hummock-hollow microtopophraphy. In addition, central poor fens tend to occur in the Central Sand Plains where open bogs are uncommon to rare. Open bogs may seem superficially similar to bog relicts, which are usually minerotrophic rather than strongly acidic and are found in southeast Wisconsin. In fact, most "bogs" in southern Wisconsin are probably more correctly classified as bog relicts. Open bogs may also resemble patterned peatlands, especially the more acidic, Sphagnum-influenced ridges (strings), but they lack the minerotrophic hollows (flarks) and patterning usually evident on aerial photos.
Because Curtis's Vegetation of Wisconsin (1959) and related data did not focus on non-forested wetlands, early ecologists simply classified open peatlands as calcareous fens, sedge meadows, or open bogs, and the various types of communities recognized today were not differentiated. Thus, older data (and maps of open bog locations) need to be reevaluated using the current natural community classification.
