Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Tep 4, distinct, spreading; stamens 4, hypogynous; filaments slender; anthers introrse; ovary bilocular, with 2-lobed style and 2 ovules per locule; berry globose, 1–2-seeded; low herbs from a slender rhizome, the erect stem with a few lvs and a short terminal raceme of small white fls. 3, N. Temp.