Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Bractlets of the epicalyx 3, narrowly linear, persistent; pet large; stamen-column bearing anthers at the summit; carpels numerous, 2–4-seeded, at maturity rounded at the summit, dehiscent to the base, thin-walled and plane on the sides, densely hirsute on the back with long, erect, simple hairs; branching perennial herbs with large, thin, palmately lobed, maple-like lvs and handsome fls solitary or fascicled in the upper axils. 7, U.S.