This northern (circumboreal) species of wet meadows and open woods on base-rich soils is rare to absent in most of Ky., Tenn. and more southeastern states (K, NS, W). It may have been overlooked in low meadows and roadsides; but there are few recent records. See also notes under graminea, which has been confused. S. longifolia differs from graminea as follows (FNA 5, W): sepals 3.5-4.5 mm long (versus 4.5-5.5 mm), weakly 3-nerved (versus strongly; seeds 0.7-1.0 mm long (versus 0.8-1.2 mm), obscurely sculptured and appearing almost smooth (versus coarsely tuberculate); inflorescence more compact, fewer-flowered. Vegetative differences are less clearcut: longifolia stems are mostly 10-35 cm tall (versus 20-90 cm), with angles minutely papillate-scabrid (versus smooth); leaves are mostly 1-3 mm wide (versus 1-6 mm) and widest at or beyond middle (versus near base), with base attenuate (versus rounded) and apex acuminate to acute (versus acute); leaf margins are minutely papillate-scabrid (versus glabrous or often ciliate near base).