This is close to hirsutella, and there has been some confusion, but recent analysis has confirmed the distinction of these two species (Smith & Waterway 2008a). C. complanata is more southern and generally occurs on seasonally damp lowlands or swales. The only consistent observable difference is that leaves are glabrescent, especially on adaxial surfaces; hirsutella has blades more uniformly and densely pilose, at least on lower leaves (FNA 23; T.W. Smith, pers. comm). Perigynia of complanata tend to be "olivaceous" (F) and have less distinct nerves (Cr). It has also been confused with caroliniana (or even considered transitional), due to its relatively smooth leaves and perhaps other characters.