Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Sep ascending or erect, blunt; pet yellow or white, rounded, emarginate, or rarely bifid, narrowed below to a claw, or in some spp. reduced or wanting; anthers short, oval or oblong; ovary ovoid, with 2–many ovules per locule; style short or none; stigma capitate; glands various; fr a silicle, seldom 5 times as long as wide; herbs with entire to dentate lvs, the hairs simple to branched or stellate. 350, mostly cool N. Hemisphere, 65 in S. Amer.