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, solitary or in short spikes from the upper axils, forming terminal spikes or spike-like panicles; sep 5, pubescent, incurved in fl, persistent and incurved over the fr, and developing dorsal appendages; stamens 5; ovary depressed-globose; styles filiform; seed horizontal, the embryo annular; shrubs or annual herbs with much-branched stems, numerous small, hairy lvs, and minute fls, villous at least in the infl. 20, Old World.