| 1 | Plants small (dwarfed), aerophores obscure, only present on base of stipe. |
| 1' | Plants not dwarfed, aerophores distinct, present from base of stipe to the rachis |
| 2 | Pinnae stalked, apex of sterile lamina usually terminated by a pinna conform to lateral ones |
| 2' | Pinnae subsessile or base adnate; apex of sterile lamina usually pinnatifid |
| 3 | Lowermost pinnae gradually abbreviated |
| 3' | Lowermost pinnae not abbreviated, or only 1 to 2 pairs shorter |
