Annual to short-lived perennial, diffusely branched, spreading or ascending, 2-5 dm, glabrate to hairy; principal lvs pinnately compound; lfls 7-11, oblong to cuneate- obovate, 1-3 cm, crenate to sharply serrate; infl much-branched, leafy, many of the lvs pinnate, others 3-foliolate; fls yellow, 5-7 mm wide; bractlets, sep and pet subequal; stamens 10-20; style terminal; achenes smooth, the inner face with a corky thickening nearly as large as the body. Moist or wet soil; Man. to Ill. and La., w. to Wash. and N.M. Summer. (P. nicolletii)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.