Trillium flexipes Raf.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Stem 2–4 dm at anthesis; lvs broadly rhombic, at anthesis 8–15 cm, at least as wide as long, abruptly acuminate, narrowed from near the middle to a sessile base; peduncle 4–12 cm, nearly horizontal to somewhat declined; sep lanceolate, about equaling the pet; pet normally white, spreading, lance-ovate to ovate, usually obtuse, 2–5 cm; filaments short, seldom over 2(–4) mm, mostly less than a fourth as long as the whitish, 6–15 mm anthers; ovary white or pinkish, flask-shaped, sharply 6-angled; 2n=10. Moist or wet woods, often in calcareous soil; Mich. to Minn., s. to n. Ark., n. Ala., and nw. Ga., and rep. from c. N.Y. Apr.–June. (T. declinatum, a preoccupied name; T. gleasonii)