| 1. Spur club-shaped, ± straight; lip generally oblong |
| P. stricta |
| 1' Spur generally cylindric, ± curved; lip base wider than tip |
| |
| 2. Perianth white to cream; lip abruptly wider below middle, ± oblong above middle |
| P. leucostachys |
| 2' Perianth green to yellow-green; lip ± gradually tapered to tip |
| |
| 3. Column generally 1.52 mm; lip generally 47 mm; spur tip blunt; inflorescence generally 515 cm, dense |
| P. hyperborea |
| 3' Column generally 2.54 mm; lip generally 610 mm; spur tip acute; inflorescence generally ± 1540 cm, open (especially below) |
| P. sparsiflora
|