Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Sep soon deciduous; outer pet imbricate, inner smaller, valvate; pollen in tetrads, uniaperturate; pistils (1–)3–15, usually only 1–3 maturing; ovules several or many; fr fleshy, aromatic; shrubs or small trees with deciduous lvs. 10, e. U.S.