Orchidaceae, the Orchis Family
Herbs, with irregular flowers, one petal, the lip, differing from the others in size and shape, inferior ovary, and one or two stamens adherent to the style.
| 1a. Flowers in a spike-like obviously twisted raceme; small, yellowish or greenish-white, in late summer and autumn (except 4a) (Ladies’ Tresses) — 2. | |
| 1b. Flowers solitary or in clusters, but never in a twisted raceme — 5. | |
| 2a. Flowers in 1 row | Ladies’ Tresses, Spiranthes gracilis. |
| 2b. Flowers in several rows — 3. | |
| 3a. Lip constricted near the apex | Ladies’ Tresses, Spiranthes romanzoftiana. |
| 3b. Lip not constricted — 4. | |
| 4a. Lip yellow; flowers in spring and early summer | Ladies’ Tresses, Spiranthes lucida. |
| 4b. Lip white | Ladies’ Tresses, Spiranthes cernua. |
| 5a. Brown, purple, or yellow plants, without green color, with scale-like leaves (1-4 dm. high; summer) (Coral Root) — 6. | |
| 5b. Plants with normal green color — 9. | |
| 6a. Lip white, not spotted | Coral Root, Corallorrhiza trifida. |
| 6b. Lip white, spotted with red — 7. | |
| 7a. Lip distinctly 3-lobed | Coral Root, Corallorrhiza maculata. |
| 7b. Lip entire, or barely toothed — 8. | |
| 8a. Flower, exclusive of ovary, 4 mm. long | Coral Root, Corallorrhiza odontorhiza. |
| 8b. Flower about 10 mm. long. | Coral Root, Corallorrhiza striata. |
| 9a. Leaf 1 or none at flowering time — 10. | |
| 9b. Leaves a single pair, basal, or opposite on the stem; never alternate on the stem — 19. | |
| 9c. Leaves several, all basal, prominently net-veined, and frequently blotched with white (scape 1-4 dm. high; flowers whitish, pubescent, in summer) (Rattlesnake Plantain) — 26. | |
| 9d. Leaves 2 or more, on the stem — 28. | |
| 10a. Foliage leaf absent or undeveloped at flowering time, or merely persisting through the winter from the previous year — 11. | |
| 10b. Foliage leaf present at flowering time — 12. | |
| 11a. Flower rose-purple, 3-5 cm. long, solitary or two (1-3 dm. high, early summer) | Arethusa, Arethusa bulbosa. |
| 11b. Flowers purplish-green, in racemes, with a spur 2 cm. long | Crane-fly Orchis, Tipularia discolor. |
| 11c. Flowers yellowish, purple tinged, in racemes; spur none (3-4 dm. high, early summer). | Putty Root, Aplectrum hyemale. |
| 12a. Leaf linear or linear-lanceolate — 13. | |
| 12b. Leaf of a broader shape — 14. | |
| 13a. Flower solitary or two; leaf just below the flower — 11a. | |
| 13b. Flowers in a loose raceme, sometimes only 2; leaf basal | Calopogon, Calopogon pulchellus. |
| 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 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 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. |
| 36a. Flower-stalk without bracts below the raceme; flowers yellowish-green | Rein Orchis, Habenaria hookeri. |
| 36b. Flower-stalk bearing bracts below the raceme; flowers greenish-white — 37. | |
| 37a. Spur 15-25 mm. long | Rein Orchis, Habenaria orbiculata. |
| 37b. Spur 30-50 mm. long | Rein Orchis, Habenaria macrophylla. |
| 38a. Lip fringed (Fringed Orchis) — 43. | |
| 38b. Lip not fringed (Rein Orchis) — 39. | |
| 39a. Lip with 2-3 evident teeth at apex — 40. | |
| 39b. Lip without apical teeth — 41. | |
| 40a. Stem-leaves 3 or more | Rein Orchis, Habenaria bracteata. |
| 40b. Stem-leaves 2 — 35b. | |
| 41a. Flowers white | Rein Orchis, Habenaria dilatata. |
| 41b. Flowers greenish-yellow — 42. | |
| 42a. Lip lanceolate, tapering toward the apex | Rein Orchis, Habenaria hyperborea. |
| 42b. Lip oblong, truncate at the apex | Rein Orchis, Habenaria flava. |
| 43a. Lip deeply 3-lobed, toothed or fringed — 44. | |
| 43b. Lip not 3-lobed, but deeply fringed — 46. | |
| 44a. Flowers purple | Purple Fringed Orchis, Habenaria psycodes. |
| 44b. Flowers white or nearly so — 45. | |
| 45a. Spur 3 cm. long or more | Prairie Fringed Orchis, Habenaria leucophaea. |
| 45b. Spur 1-1.5 cm. long | Ragged Fringed Orchis, Habenaria lacera. |
| 46a. Flowers yellow | Yellow Fringed Orchis, Habenaria ciliaris. |
| 46b. Flowers white | White Fringed Orchis, Habenaria blephariglottis. |