Sparingly branched, 3-8 dm, glabrous or nearly so; basal lvs simple, broadly ovate, usually cordate at base, or occasionally ternate like the cauline; cauline lvs ordinarily pinnate with 3(5) ovate or lanceolate, toothed lfls 4-8 cm, rarely the lateral lfls again 2-3-lobed; umbels long-peduncled, 3-8 cm wide, the 6-10 rays unequal; fr ellipsoid, 3.5-5 mm, three-fourths as wide, including the broad wings; 2n=22. Woods, R.I. to Minn. and S.D., s. to Ga., La., and Okla. May, June. Typical T. trifoliatum (T. atropurpureum), with dark purple fls, is widespread, but more common eastward. Yellow-fld plants, usually distinguished as var. flavum S. F. Blake (T. aureum, misapplied), are also widespread, but more common westward.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.