Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Sep 2, herbaceous, ovate, persistent in fr; pet 5, oval or elliptic, spreading; stamens 5, opposite the pet; ovules 6; style with 3 short lobes; capsule ovoid, opening by inrolling valves; perennial herbs from a rounded corm (our spp.) or fleshy taproot, with one or few lvs from the base and a single opposite pair on the stem below the loose terminal raceme; our spp. have delicate glabrous stems 1–3 dm from the corm, lengthening during and after anthesis, the 5–15 long-pediceled fls with pink-veined, otherwise white or pale pinkish (yellow) pet 1–1.5 cm. 10, N. Amer.