Annual 0.5-3 dm, simple or branched especially below; main lvs oblong or linear-oblong to oblanceolate, 0.5-3 cm נ1-8 mm, irregularly toothed or entire; infl terminal, elongate, lax; bracts alternate, gradually reduced upwards, often not much different from the lvs, each subtending a single subsessile fl; cor white or whitish, only 2 mm wide; mature pedicels 1-2 mm; fr 3-4 mm, ±obcordate, the notch varying in depth; style very short, 0.1-0.3 mm; seeds numerous, 0.4-0.8 mm; 2n=52. Moist places; temperate N. and S. Amer., and intr. in Europe. Apr.-Sept. Our common form, the var. peregrina, is glabrous. The chiefly western var. xalapensis (Kunth) H. St. John, has the stem and commonly also the sep and frs ±pubescent with short, gland-tipped hairs; it reaches the w. edge of our range, and extends e. to the Atlantic along our n. border.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.