This northeastern taxon is close to effusus. Although recognized as a variety by some (F) and a species by others (Cr), pylaei was not distinguished at all in FNA 22, which is surprising given the fine divisions recognized in the tenuis group. It has been overlooked in Appalachian regions, where it is locally common in thin woods and boggy openings along streamheads, seeps and similar places with wet acid infertile soils. It is typically absent from old fields, where effusus var. solutus is often locally dominant in swales. J. pylaei differs from effusus var. solutus (F, Cr) in its usually narrower culms (ca. 2-3 mm at summit versus 3-4 mm), with fewer (ca. 10-20 versus 30-60), distinctly coarser ridges, often smaller heads (usually 2-6 cm wide versus 4-10 cm), and usually longer sepals (ca. 2.5-4 mm versus 2-3 mm), which exceed (versus equal) petals and capsule.