Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Sep and lateral pet similar, 5–7-veined; lip 3-lobed, usually with 5–7 longitudinal ridges convergent below and extending nearly to the tip; lateral lobes of the lip upturned and partly embracing the fleshy, distally dilated column; anther terminal, with 8 pollinia, yellowish or brownish to purplish, nongreen mycotrophs arising from a cluster of coralloid rhizomes; stem bearing a few sheathing scales and a loose terminal raceme of dull yellow fls striped with purple. 7, N. Amer., esp. Mex.