Perennial 2-10 dm from deep-seated creeping roots, glabrous or glabrate; lvs elongate, 5-18 cm נ6-35 mm, entire, or the lower ones ±lobed, rarely sharply denticulate, often glaucous beneath; heads several or numerous, very showy, with 18-50 blue fls; invol 15-20 mm in fr; achenes 4-7 mm overall, the slender body moderately compressed, prominently several- nerved on each face, the beak stout, often whitish, up to as long as the body; 2n=34. Mostly in meadows, thickets, prairies, and other moist low places; Alas. to Calif., e. to Minn. and Mo., and occasionally intr. eastward. June-Sept. (L. tatarica ssp. p.; L. oblongifolia)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.