Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Sep erect, the outer narrow, crested to near the summit, the inner broad, saccate at base; pet purple to white, the blade obovate, the claw surpassing the cal; short stamens subtended by a U-shaped gland; long stamens glandless; anthers linear-oblong; ovary cylindric; style scarcely narrower; stigma 2-lobed, decurrent along the style; ovules numerous; frs widely spreading on stout pedicels, linear, terete or nearly so, scarcely dehiscent; stigma persistent; valves indistinctly 1-nerved; seeds large (3–4 mm), angularly fusiform, in one row; tall biennial or perennial herbs with showy fls; pubescence of both simple and branched hairs. 25, Eurasia.