13a. Flower solitary or two; leaf just below the flower --11a.

13b. Flowers in a loose raceme, sometimes only 2; leaf basal =Calopogon, Calopogon pulch.e.l.lus.=

14a. Flowers greenish, yellowish, or white --15.

14b. Flowers pink to purple, often variegated --17.

15a. Flowers 6-10 mm. wide, with a spur about the same length (1-4 dm.

high, summer) (Rein Orchis) --35.

15b. Flowers 5 mm. wide or less; spur none (1-2 dm. high; summer) (Adder's Mouth) --16.

16a. Pedicels less than 5 mm. long; lip broadest below the middle =Adder's Mouth, Microstylis monophyllos.=

16b. Pedicels more than 5 mm. long; lip broadest near the apex =Adder's Mouth, Microstylis unifolia.=

17a. Flowers spicate; lip distinctly 3-lobed (1-2 dm. high; early summer) --24.

17b. Flowers solitary or two --18.

18a. Leaf on the stem, lanceolate to ovate --34a.

18b. Leaf basal, round-ovate (2 dm. high or less; early summer) =Calypso, Calypso bulbosa.=

19a. Leaves opposite and sessile near the middle of the stem (1-3 dm.

high; flowers in summer) (Tway-blade) --20.

19b. Leaves basal --21.

20a. Lip deeply 2-cleft (flowers purplish) =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 p.u.b.escens.=

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. p.u.b.escens.=

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 spurred --33.

32b. Flowers in terminal racemes, spurred --38.

33a. Leaves a whorl of 5 (2-3 dm. high; petals greenish; late summer) =Whorled Pogonia, Pogonia verticillata.=

33b. Leaves alternate --34.

34a. Leaves lanceolate or narrowly ovate, 2-8 cm. long, narrowed at base; flower terminal (1-4 dm. high; flowers pink purple, early summer) =Snake Mouth, Pogonia ophioglossoides.=

34b. Leaves ovate, 1-2 cm. long, clasping; flowers axillary (5-20 cm. high; flowers purple, summer) =Nodding Pogonia, Pogonia trianthophora.=

35a. Leaf basal; spur nearly straight =Rein Orchis, Habenaria obtusata.=

35b. Leaf on the stem; spur strongly curved =Rein Orchis, Habenaria clavellata.=