=Tway-blade, Listera cordata.=

20b. Lip wedge-shape, with 2 round shallow lobes (flowers
greenish-yellow) =Tway-blade, Listera convallarioides.=

21a. Lip an inflated sac about 4 cm. long --29d.

21b. Lip not sac-like --22.

22a. Flower with a spur 15-50 mm. long --23.

22b. Flower not spurred (1-2 dm. high; early summer) (Tway-blade)
--25.

23a. Flowers purple or magenta, or with white markings --24.

23b. Flowers greenish, yellowish, or white (1-4 dm. high; summer) (Rein
Orchis) --36.

24a. Leaf 1 (1-2 dm. high; early summer)
=Round-leaved Orchis, Orchis rotundifolia.=

24b. Leaves 2 (-20 cm. high; late spring)
=Showy Orchis, Orchis spectabilis.=

25a. Lip about 10 mm. long, purple =Tway-blade, Liparis liliifolia.=

25b. Lip about 5 mm. long, yellowish-green
=Tway-blade, Liparis loeselii.=

26a. Perianth 8-10 mm. long; lip with elongated point
=Rattlesnake Plantain, Epipactis decipiens.=

26b. Perianth 4-6 mm. long; lip sack-like --27.

27a. Raceme loosely flowered, one-sided
=Rattlesnake Plantain, Epipactis repens var. ophioides.=

27b. Raceme closely flowered, not one-sided
=Rattlesnake Plantain, Epipactis pubescens.=

28a. Lip conspicuously sack-like, inflated (late spring and early
summer) (Lady's Slipper) --29.

28b. Lip not sack-like nor inflated --32.

29a. Lip white (1-3 dm. high)
=White Lady's Slipper, Cypripedium candidum.=

29b. Lip yellow (2-7 dm. high) --30.

29c. Lip white, with crimson or purple markings --31.

29d. Lip pink (1-4 dm. high, late spring)
=Stemless Lady's Slipper, Cypripedium acaule.=

30a. Lip 2-3 cm. long.
=Small Yellow Lady's Slipper, Cypripedium parviflorum.=

30b. Lip 3.5-5 cm. long
=Large Yellow Lady's Slipper, Cypripedium parviflorum var. pubescens.=

31a. Lip 2 cm. long or less; sepals separate (1.5-3 dm. high)
=Ram's Head Lady's Slipper, Cypripedium arietinum.=

31b. Lip 3 cm. long or more; the 2 lower sepals united
=Showy Lady's Slipper, Cypripedium hirsutum.=

32a. Flowers solitary in the axils, or solitary and terminal; not
spu