Stem leafy, 2-8 dm; lvs ±sheathing, oval to lance-ovate, 6-20 cm, half as wide; fls 1 or 2, each subtended by an erect foliaceous bract; sep and lateral pet greenish-yellow to purplish-brown; upper sep ovate to lance-ovate, sharply acute, 3-8 cm; united lower sep somewhat narrower, 2-toothed at the tip; lateral pet lanceolate, 3-8 cm, usually twisted; lip yellow, usually veined with purple, 2-5 cm; 2n=20. Circumboreal, s. in Amer. to S.C., La., and N.M. May-July. Two vars. in N. Amer., partly isolated by differences in pollinators associated with fl-size.

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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