Plants 24-80 cm. Leaves few-several, abruptly diverging or sometimes ascending, scattered along stem; blade oblong to ovate or lanceolate, 5.5-16(-28) × 1-4.5 cm. Spikes very lax to dense, flowers sometimes irregularly grouped in fascicles. Flowers resupinate, not showy, green to yellowish green, often suffused with blue or lip sometimes with red; lateral sepals spreading to reflexed; petals ovate- to lance-falcate, margins entire; lip descending to somewhat reflexed or projecting, lanceolate to ovate, sometimes with prominent suborbiculate basal dilation, without basal thickening, 4-8 × 1.5-3 mm; spur strongly clavate to scrotiform, 2-3 mm, apex obtuse; rostellum lobes strongly diverging, very small, rounded, obscure; pollinaria straight; pollinia remaining enclosed in anther sacs; viscidia orbiculate to oblong; ovary rather slender to stout, mostly 5-9 mm. 2n = 42 .
Flowering Jul--Aug. Stream banks, shores, ditches, fens, seeping slopes, roadsides, commonly in thickets, open woods; 2500--3300 m; Ariz., Calif., Colo., N.Mex., Wyo.
Flowers of Platanthera purpurascens are strongly semen scented, and their musty scent is markedly different than the sweet and spicy scents of other fragrant species.
In some areas this species hybridizes with Platanthera dilatata var. albiflora, producing sweetly fragant plants with lanceolate green lips. At the southern edge of its range, however, it often occurs with similar plants in the absence of another putative parent. The identity of these plants is uncertain. Their rather generalized morphology might mask polyphyletic origins.