Segregates within this widespread southeastern species were generally recognized during 1900-1950 (Sm, F), but rarely since then (from B to W). Colls. from CLIN (GH), MUHL (KY) and WAYN (GH) have been called S. biflora var. hispidissima (Michx.) Pollard & Ball, with the stem more pubescent. Plants formerly referred to S. riparia Kearney may be concentrated in north-central counties, with colls. from CLAR, ESTI, GARR, HARD, MADI and MEAD. S. riparia has been considered to differ in its less ascending habit; its leaves smaller (ca. 0.5-2.3 cm long versus 1.5-4 cm) and oval to oblanceolate (versus lanceolate); and its bracteal leaves with smooth (versus usually bristly-hispid) bases and with eciliate (versus bristly-ciliate) blades. There are no clear differences in range or habitat, based on current data. S. riparia was initially described from along the French Broad Rv. in Tenn.