Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Sep 3, herbaceous, green or anthocyanic; pet 3, all alike, obovate to elliptic, blue or pink (white); stamens 6; filaments usually villous; ovary 3- locular, with 1–2 ovules per locule; style slender; stigma capitate; fr loculicidal; perennial herbs, usually somewhat succulent, with elongate, linear to lanceolate lvs dilated into conspicuous basal sheaths, the umbel-like cymes of several to many handsome fls subtended by elongate foliaceous bracts (except for the last sp.). Except for T. virginiana, our spp. bloom in summer and early fall. 50, New World.