Plants 38-85 cm. Leaves several to many, ascending, scattered along stem, imperceptibly reduced to bracts distally; blade lanceolate to ovate-lanceolate, to 26 × 5 cm. Spikes lax. Flowers resupinate, showy, creamy white; lateral sepals somewhat porrect; petals flabellate, truncate, sometimes emarginate, apically lacerate; lip descending, deeply 3-lobed, without basal thickening, 17-32 × 20-39 mm, distal margins of lobes deeply incised and fringed, lateral lobes flabellate, sometimes broadly and overlapping middle lobe, middle lobe flabellate, sometimes very broadly, emarginate; spur slenderly clavate, 36-55 mm; rostellum lobes directed strongly forward, wide-spreading, angular; pollinaria geniculate; pollinia directed forward (column appearing hooded), remaining enclosed in anther sacs; viscidia orbiculate; ovary slender, mostly 20-30 mm. 2n = 42. Flowering (May--)Jun--Aug. Mesic to wet prairies; of conservation concern; 200--800(--1600 m); Man.; Iowa, Kans., Minn., Mo., Nebr., N.Dak., Okla., S.Dak., Wyo. In Platanthera praeclara the wide-spreading rostellum lobes separate the viscidia by 6-7.5 mm, whereas in P. leucophaea the short rostellum lobes are more nearly parallel, and the viscidia are separated only by about 1-3.5 mm. These differences are immediately obvious on living material, but the measurements are nearly always impossible in herbarium specimens. In Wyoming Platanthera praeclara is known from a single, much higher station outside the usual range.
Infl avg shorter and fewer-fld; fls larger, the lateral pet mostly 11-15 נ7-11 mm, the lip 22-30 mm, the spur 40-50 mm, column larger, somewhat angular, the pollinaria well spaced, their caudicles widely diverging and directed somewhat forward; more western, extending e. to Minn., Io. and e. Mo.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.