Matted perennial, strict and branched from the base or diffusely branched throughout, 2-8 dm; stems smooth on the angles but densely short-bearded at the nodes; principal lvs in 4's, linear to lanceolate or oblanceolate, 10-30 נ1-6 mm, obtuse, the margins and the midvein beneath usually ±scabrous or hispid-ciliolate; infls short, almost all terminal, with 3-5 fls on short ascending pedicels, the pedicels in fr 5-10 mm, divaricate, stiff, smooth; fls white, 4-merous, 2-3.5 mm wide, the lobes longer than wide; frs 4-5 mm, ±tuberculate, often only one mericarp developed; 2n=48. Swampy thickets and moist meadows; N.S. and s. Que. to Minn. and S. D., s. to Fla. and Tex.
May-July. (G. tinctorium, misapplied) The widespread var. obtusum has the lvs mostly (2)3-5 mm wide, and has consistently bearded nodes. The var. filifolium (Wiegand) Fernald, from s. N.J. to Ga., often near the coast, has lvs mostly 1-2 mm wide, and the nodes are not always bearded.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.