Peatland communities in the sub-boreal region of Minnesota and western Wisconsin were characterized by floristic composition, structure and environmental characteristics to determine the natural variation among peatland communities in the region and their shared associations with the boreal and temperate peatlands of North America. Floristic classification revealed five, distinct peatland community types, identified as Sphagnum Bogs, Herbaceous Fens, Forested Fens, Rich/Calcareous Fens and Phalaris anrundinacea —dominated peatlands. Differences among sub-boreal peatlands largely reflected changes in the significant indicator and dominant plant species identified, which were found to exhibit high fidelities to a particular peatland community type. Floristic variations among sub-boreal peatlands were observed to correlate with changes in pore-water chemistry along a strong pH-alkalinity gradient. Ordinal analysis by non-metric multidimensional scaling also indicated a strong community association with soil and pore-water chemistry, which primarily reflected the geomorphic and hydrologic settings in which communities developed and the transitional nature of the region. In addition, the broad physiological tolerance and invasive nature of P. anrundinacea was found to pose a substantial threat to the biodiversity and ecological functioning of sub-boreal peatland communities.