| | 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 1.5–2 mm; lip generally 4–7 mm; spur tip blunt; inflorescence generally 5–15 cm, dense |
| P. hyperborea |
| | 3' Column generally 2.5–4 mm; lip generally 6–10 mm; spur tip acute; inflorescence generally ± 15–40 cm, open (especially below) |
| P. sparsiflora
|