Bot. North. Middle States, 347. 1833.
Plants 11–130 cm or more. Leaves few–several, ascending to recurved-spreading, scattered along stem, gradually reduced to bracts distally; blade linear, linear-lanceolate, oblong, or oblanceolate, 3.5–32 × 0.3–7 cm. Spikes very lax to very dense. Flowers resupinate, rather showy, conspicuous, white; lateral sepals spreading to reflexed; petals ovate- to linear-lance-falcate, margins entire; lip descending or apex adhering to dorsal sepal and petal apices, linear-lanceolate to lanceolate, without basal thickening, 4–11 × 2–5 mm, base slightly rounded-dilated to orbiculate, rarely rhombic, margins entire; rostellum lobes parallel to slightly divergent, directed downward, very small, obscure, rounded; pollinaria straight; pollinia remaining enclosed in anther sacs; ovary rather slender to stout, 5–15 mm. 2n = 42.
Varieties 3 (3 in the flora).
|1||Spur shorter than lip, clavate to slightly capitate.||Platanthera dilatata var. albiflora|
|1||Spur nearly equaling to exceeding lip, slender to slightly clavate.||> 2|
|2||Spur about equal to lip (mostly within 2 mm).||Platanthera dilatata var. dilatata|
|2||Spur markedly exceeding lip (commonly 11/2 or more times length of lip).||Platanthera dilatata var. leucostachys|