Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Fls perfect; sep 5, distinct; stamens 3–10; ovary superior, 3–5-locular; styles 3–5; ovules many; fr a thin-walled loculicidal capsule; seeds without an aril; herbs with opposite or whorled lvs and pedicellate, axillary, white or greenish fls. 20, warm reg.