Essentially a plant of the open. Mostly in sandy soil in prairies, marshes, and low borders of lakes and in roadside ditches. Frequent in the lake and prairie areas, becoming infrequent to rare in the southern counties where its habitat is rare.
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.