This northeastern species has been confused in nomenclature with tonsa or umbellata, and should perhaps be treated a variety of tonsa (FNA 23); further revision is needed (W). In Ky. rugosperma is restricted to dry sandy soils, especially on open sandstone clifftops. Both rugosperma and tonsa are distinct from umbellata in their generally longer perigynia (3-4.7 mm versus 2.2-3.3 mm), with longer beaks (0.9-2 mm versus 0.4-1 mm). Also, their leaves are often relatively wide (up to 4.3 mm versus 2.3 mm), short (sometimes equalled by stems versus never in umbellata), bright-green and coriaceous. Typical tonsa has perigynia with fewer hairs (restricted to base of beak), and its leaves are relatively short (not exceeding culms by much), paler green, more coriaceous and usually smooth above (versus scabrous to papillose). It is somewhat more northern and needs further verification in Ky., but it has been recently reported by Naczi et al. (2015), with colls. at NY from LEWI, MADI, MCRE and ROCK.