Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Epicalyx wanting; stamen-column with anthers at the top; carpels 5– many; ovules 3–9 per carpel; styles 5–many, slender, stigmatic at the top; mature carpels dehiscent across the top, rounded or beaked at the summit, eventually falling from the axis; herbs or shrubs, usually pubescent, with broad, cordate, angular or lobed lvs and axillary, usually yellow fls. 100+, warm reg.