Erect, glabrous, virgately branched perennial 4-8 dm, the stem 4-angled; lvs thick and firm, sessile, linear-oblong to lance-ovate, usually only the lowest opposite, those
below the branches to 4 cm, broadest below the middle or near the truncate to broadly rounded or subcordate base, those of the branches crowded, proportionately narrower, obtuse to rounded at the base; fls solitary in most of the upper axils, heterostylic, either the stamens or the style exserted; pedicels 1-3 mm; hypanthium 4-7 mm, sharply but narrowly 12-winged; intersepalar appendages twice as long as the sep; pet purple, obovate, 2-6 mm; disk present; 2n=20. Moist or wet soil, especially on prairies; Me. to N.D. and se. Wyo., s. to Fla. and Tex., and locally elsewhere, perhaps as an introduction. June-Sept. Most of our plants are var. alatum, as described above. (L. dacotanum) Var. lanceolatum (Elliott) Torr. & A. Gray, more robust, to 12 dm, with lanceolate lvs narrowed to the base, is chiefly more southern, barely reaching our range in se. Va.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.