Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Pet white, pink, or purple, broadened distally; stamens 4–8, as many as the pet; styles usually 3, bipartite to the base; ovules in 2–5 rows on each placenta; capsule usually 3-valved; testa loose; lf-blades filiform to peltate; stipules scarious, variously fringed or divided, or rarely wanting; infl a sympodial cyme, nodding at the undeveloped tip. 100, widespread.