Erect, divergently branched annual, 1-4 dm; lvs linear to linear-oblong, 1-2(-3) cm נ1-3 mm, at least the lower (sometimes all) in whorls of 2-5; lower branches of the infl usually opposite or whorled; peduncle elongate; racemes continuous, conic or cylindric- conic, the floriferous and fructiferous part 6-15 mm, appearing truncate at base, the whole axis to 4 cm; fls white, greenish, or occasionally pinkish, the lower dropping promptly as the fr matures; wings half to two-thirds as long as the fr; 2n=34. Moist, sandy soil, grasslands, and woods. July-Oct. Var. isocycla Fernald, occurring nearly throughout the range of the sp. (Vt. to Man., s. to Fla. and Tex.) has finely pubescent seeds, short pedicels a fourth to a third as long as the fr, greenish-white sep, narrow, dense racemes on peduncles 0.5-4 cm, the plant with widely spreading branches. Var. verticillata, occurring from Me. to Mich., s. to Tenn., has hirsute seeds, pedicels a third to half as long as the fr, often purplish sep, wider, looser racemes on peduncles 2-7 cm, and the branches are ascending.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.