Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Perianth 6-parted to the top of the ovary, narrowly campanulate, its segments nearly erect, persistent in fr, the sep shorter and narrower than the pet; stamens 3, exsert, erect, attached to the base of the pet; anthers contorted when dry; ovary wholly inferior; fr subglobose; seeds few in each locule, rounded or quadrate, flat, attached at the middle; sap red. Monotypic.