1	Lip lobed, fringed, eroded, lacerate, or emarginate.		(2)
+	Lip entire, at most abruptly dilated toward base (in some robust Alaskan material of P. dilatata var. albiflora basal dilation of lip is elaborated forward, taking form of lateral lobules).		(15)
2 (1)	Lip deeply and subequally 3-lobed (lateral lobes each in area equaling approximately 1/2 middle lobe, often much more).		(3)
+	Lip not deeply, subequally 3-lobed, merely auriculate, fringed, eroded, lacerate, or emarginate, or apically shallowly 3-lobed.		(8)
3 (2)	Petals linear-oblong to oblong-spatulate, usually entire; lip greenish white.		24 Platanthera lacera
+	Petals oblong-obovate to flabellate, lacerate toward apex; lip pure white or pink-magenta to lavender.		(4)
4 (3)	Lobes of lip dentate to dentate-lacerate, not fringed; rostellum lobes spreading.		19 Platanthera peramoena
+	Lobes of lip fringed; rostellum lobes spreading or parallel.		(5)
5 (4)	Flowers pink-magenta to lavender, rarely white; pollinia erect; pollinaria nearly straight; column appearing truncate in lateral view.		(6)
+	Flowers white; pollinia directed forward; pollinaria geniculate; column appearing hooded in lateral view.		(7)
6 (5)	Rostellum lobes spreading, angular in lateral view.		20 Platanthera grandiflora
+	Rostellum lobes parallel, rounded in lateral view.		21 Platanthera psycodes
7 (5)	Rostellum lobes spreading, angular in lateral view.		22 Platanthera praeclara
+	Rostellum lobes parallel, rounded in lateral view.		23 Platanthera leucophaea
8 (2)	Lip basally auriculate, or apically emarginate or shallowly lobed.		(9)
+	Lip fringed or eroded.		(10)
9 (8)	Lip with basal pair of auricules flanking prominent tubercle on adaxial surface, apex obtuse to emarginate.		18 Platanthera flava
+	Lip without basal pair of auricles or tubercle, apex shallowly 3-lobed.		31 Platanthera clavellata
10 (8)	Lip not conspicuously fringed, merely eroded to lacerate.		(11)
+	Lip conspicuously fringed.		(12)
11 (10)	Flowers white; lip 10–15 mm.		26 Platanthera integrilabia
+	Flowers yellow to orange; lip less than 6 mm.		32 Platanthera integra
12 (10)	Rostellum lobes triangular, apices directed forward (column appearing acute in lateral view).		(13)
+	Rostellum lobes slender, directed downward toward apices (column appearing truncate in lateral view), straight to distally retrorse.		(14)
13 (12)	Flowers white.		25 Platanthera blephariglottis
+	Flowers orange.		27 Platanthera ciliaris
14 (12)	Spur 8–17 mm, its mouth nearly circular; rostellum lobes strongly retrorsely curved toward apices; viscidia presented downward and approximately parallel to lip.		29 Platanthera chapmanii
+	Spur 4–10 mm, its mouth triangular or keyhole-shaped; rostellum lobes scarcely to strongly curved; viscidia presented forward, nearly perpendicular to approximately parallel to lip.		28 Platanthera cristata
15 (1)	Leaves 1–2; scape naked or with 1(–2, very rarely) bracts.		(16)
+	Leaves (1–)3–several; scape with gradually reduced bracts distially.		(21)
16 (15)	Spur saccate to stoutly cylindric; lip broadly elliptic-suborbiculate to obovate, concave.		17 Platanthera chorisiana
+	Spur slender; lip linear to rhombic-lanceolate, ± flat.		(17)
17 (16)	Leaf 1, or if 2 alternate and widely spaced on stem, erect-spreading.		(18)
+	Leaves 2 in basal pair, wide-spreading, commonly lying on ground.		(19)
18 (17)	Lip linear to linear-rhombic-lanceolate (lanceolate in subsp. oligantha); spur tapering from broad base, ± as long as lip; widespread.		4 Platanthera obtusata
+	Lip elliptic to elliptic-oblong or elliptic-lanceolate; spur cylindric to clavate, ± 2 times as long as lip; w Aleutian Islands.		5 Platanthera tipuloides
19 (17)	Scape naked; lip directed forward, lanceolate; spur tapering to apex from broad base.		3 Platanthera hookeri
+	Scape with 1 or more bracts; lip pendent, linear to linear-oblong; spur clavate.		(20)
20 (19)	Spur less than 28 mm; pollinaria less than 4.6 mm.		1 Platanthera orbiculata
+	Spur equal to or greater than 28 mm; pollinaria equal to or greater than 4.6 mm.		2 Platanthera macrophylla
21 (15)	Lip uppermost (flowers not resupinate); flowers white.		30 Platanthera nivea
+	Lip lowermost (flowers resupinate); flowers white, green, or yellowish.		(22)
22 (21)	Viscidia linear to linear-oblong; flowers white; lip usually with suborbiculate to orbiculate basal dilation.		6 Platanthera dilatata
+	Viscidia oblong to orbiculate; flowers greenish, yellowish, or white; lip linear to linear-rhombic, elliptic, or lanceolate, base undilated or with obscure to orbiculate basal dilation.		(23)
23 (22)	Column comparatively large, occupying ca. 2/3 hood formed by dorsal sepal and petals; rostellum lobes widely spaced, diverging, and together with stigma and connective forming hemispheric chamber; lip linear to linear-oblong or linear-lanceolate, or narrowly elliptic, base undilated.		(24)
+	Column comparatively small, occupying less than 1/2 hood formed by dorsal sepal and petals; rostellum lobes parallel, diverging, or converging, but scarcely elevated, at most separated by narrow slit, not forming hemispheric chamber; lip linear to linear-lanceolate, rhombic-linear, rhombic-lanceolate, or elliptic, base undilated or with obscure to orbiculate basal dilation.		(26)
24 (23)	Leaves reduced; blades rigidly erect, loosely sheathing stem, scarcely spreading beyond width of inflorescence, sometimes absent; dry to mesic forest.		14 Platanthera brevifolia
+	Leaves well developed; blades prominent, spreading well beyond sheathing bases and width of inflorescence; wet-mesic to wet sites.		(25)
25 (24)	Spur 6–14 mm, 0.7–1.6 times length of lip; lip with prominent basal median ridge; leaves ascending or wide-spreading, scattered along stem.		13 Platanthera sparsiflora
+	Spur 12–17 mm, 1.3–2.6 times length of lip; lip without prominent median ridge, but often with series of obscure parallel ridges; leaves wide-spreading, usually limited to proximal portion of stem.		15 Platanthera zothecina
26 (23)	Anther low, appearing to lie atop stigma; anther sacs widely diverging from apices scarcely separated by obscure connective; flowers autogamous; pollinia rotated forward, commonly free of anther sacs and/or fragmenting into loose masses that trail downward onto stigma; spur clavate, mostly slightly shorter than lip; lip rhombic-lanceolate, yellowish to yellowish green.		10 Platanthera aquilonis
+	Anther high, rising above stigma; anther sacs more nearly parallel, converging, or diverging from apices separated by evident connective; flowers not autogamous (except evidently autogamous in P. hyperborea; see also note under P. huronensis); pollinia remaining within anther sacs; spur scrotiform or saccate to slenderly clavate or filiform, much shorter to much longer than lip; lip linear, elliptic, or broadly lanceolate, or with abrupt basal dilation, white to green or yellowish.		(27)
27 (26)	Spur 8–25 mm, much longer than lip, filiform; lip usually with small median basal thickening, linear-oblong to linear-elliptic, rarely rhombic-ovate.		16 Platanthera limosa
+	Spur 2–12 mm, much shorter to slightly longer than lip, saccate or scrotiform to capitate, clavate, or slenderly cylindric; lip linear-rhombic, linear-lanceolate, or rhombic-lanceolate, or with pronounced orbiculate to suborbiculate basal dilation.		(28)
28 (27)	Pollinaria and rostellum lobes parallel to converging toward orbiculate viscidia; spur scrotiform or saccate to spatuloid-capitate or strongly clavate, much shorter than lip.		12 Platanthera stricta
+	Pollinaria and rostellum lobes diverging toward oblong or sometimes (in P. purpurascens) orbiculate viscidia; spur slenderly cylindric to strongly clavate, saccate, or scrotiform, slightly longer to much shorter than lip.		(29)
29 (28)	Lip oblong or rarely lanceolate, dull yellowish; rostellum lobes usually projecting forward, separated by narrow slit; leaves clustered toward base of stem.		13 Platanthera sparsiflora
+	Lip broadest at base, lanceolate, ovate, or linear, or with pronounced basal dilation, white, greenish or yellowish; rostellum lobes low, not projecting forward; column without evident slit; leaves scattered along stem.		(30)
30 (29)	Lip pure white, usually with pronounced suborbiculate to orbiculate basal dilation or rarely shallowly 3-lobed; spur clavate to slightly capitate, somewhat to very much shorter than lip.		6 Platanthera dilatata
+	Lip greenish or yellowish, mostly lanceolate, ovate, or linear, sometimes obscurely or prominently dilated at base; spur slenderly cylindric to strongly clavate, saccate, or scrotiform, shorter than to slightly longer than lip.		(31)
31 (30)	Spur saccate or scrotiform to clavate-inflated (widest at apex), ca. 1/2 length of lip; lip yellowish green to dull yellowish or intensely bluish green, sometimes marked with red, linear-lanceolate to prominently rounded-dilated at base; musty scented.		11 Platanthera purpurascens
+	Spur slenderly cylindric to slenderly clavate or clavate, not inflated, merely obtuse to subacute, shorter to slighter longer than lip; lip whitish green to perhaps yellowish green in P. hyperborea; sweet scented.		(32)
32 (31)	Lip linear-rhombic, with straight sides, not at all rounded-dilated at base; spur ca. 2/3 to slightly shorter than lip; Aleutian Islands, adjacent Alaska.		9 Platanthera convallariifolia
+	Lip lanceolate to ovate, usually obscurely to prominently rounded-dilated at base; spur slightly shorter to slightly longer than lip.		(33)
33 (32)	Lip lanceolate, usually obscurely rounded-dilated at base, whitish green; spur slenderly clavate to slenderly cylindric; flowers not autogamous; pollinia retained within anther sacs (but see note); viscidia oblong; widespread.		7 Platanthera huronensis
+	Lip ovate, rarely lanceolate, abruptly and broadly dilated at base, apparently yellowish green; spur markedly clavate; flowers autogamous; pollinia rotating forward and downward from anther sacs or fragmenting and pollen masses trailing onto stigma; viscidia linear to linear-oblong; Greenland.		8 Platanthera hyperborea