Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Sep oblong, ascending; pet yellow, spatulate to obovate; short stamens partly surrounded at base by a semicircular gland; long stamens separated by a short erect gland; anthers oblong; ovary cylindric, narrowed to a slender style; ovules several per locule; stigma truncate; frs linear, terete or obscurely 4-angled, tipped by the persistent short style, the valves with strong midnerve and anastomosing intermediate nerves; biennials or short-lived perennials, glabrous or with a few simple hairs, the basal lvs mostly pinnatifid with a large terminal lobe and 2–several smaller lateral ones, the cauline smaller, entire to pinnatifid. (Campe) 20, N. Temp.