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, large, foliaceous, cordate, ± incised; stamen-tube bearing anthers along the side but not at the summit; style undivided, with 5 subsessile stigmas; ovary 3–5-locular, ripening into a loculicidal capsule; seeds covered with long, usually white fibers. 20, warm reg.