This perennial is widespread in thin swampy woods and marshy openings across eastern North America, usually on somewhat base-rich soils. If Gl is followed, most plants in Ky. are referable to the largely midwestern var. ramosum Gleason, and colls. from ADAI, LETC, JEFF (EKY) and WARR (WKY) are the more southeastern var. obtusum. However, this distinction has not been made in recent treatments (Cr, W). G. obtusum has often been confused with tinctorium, but can be distinguished (F, Cr, W) by its larger flowers (4-merous versus 3-merous) and fruits (ca. 3-5 mm long versus 2-3 mm). Stems are usually more erect (versus often reclining to low and matted) and mostly glabrous except at nodes (versus often slightly retrorse-scabrid). Leaves are mostly just 4 per node or rarely 5-6 (versus mostly 5-6 or sometimes 4) but larger (ca. 1-3 cm long versus 0.5-2 cm); 2n = 48 (versus 24).