Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Upper sep and lateral pet adherent by their margins to form a concave galea extending forward over the lip; lateral sep free, scarcely spreading except at the tip; lip shorter than the galea, ± strongly saccate or pouch-like at base, prolonged distally into a horizontal or deflexed beak; column short, bearing the anther on its back below the usually bifid rostellar tip; pollinia 2; perennial, forming new rosettes by budding from creeping rhizomes; lvs all basal, often white-reticulate, in ours narrowed to a broadly petiolar base; scape bracteate, terminating in a raceme of white or greenish fls; our spp. all with glandular hairy scape and infl, the lateral pet thin, white, differing in texture from the dorsal sep to which they adhere. 25+, cosmop.