This northeastern taxon is close to effusus. Although recognized as a variety by some (F) and a species by others (Cr, W),, 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, W), in its usually narrower culms (ca. 2-3 mm at summit versus 3-4 mm), with fewer ridges (ca. 10-20 versus 25-30 at summit) often smaller heads (mostly 2-6 cm wide versus 4-10 cm), and perianths mostly longer (ca. 2.5-4 mm versus 2-3 mm), with sepals slightly exceeding (versus equalingl) petals and capsule. W.M. Knapp & B.A. Sorrie (in W) noted that the ridges of pylaei have "firm texture; fresh, upper stems dull or matte; dried stems coarsely ridged, ridges visible in high relief at 10×, dried ridges capped with shiny bulging cells". In effusus var. solutus, ridges are "relatively inconspicuous... with a soft texture, easily compressed; fresh upper stems shiny; dried stems with lower ridges, fine or coarse, ridges visible in low relief at 10×, dried ridges capped with low dull cells".