| 1 | Spores monolete. The two branches at each fork equal; either lowland plants with ultimate branches 9-12 cm wide, or mountain plants. First fork of each vein at its very base. |
| 1' | Spores trilete. Branches at a fork in many cases unequal; ultimate branches to c. 6 cm wide. Veins never grooved on lower surface; first fork of each vein distinctly above the base. |
| 2 | Lamina not very thick nor with the veins grooved on the lower surface. |
| 2' | Lamina very thick, the veins grooved on the lower surface |
| 3 | Ultimate branches commonly 40 cm long and 9-12 cm wide; lower surface almost glabrous. |
| 3' | Ultimate branches not over 7 cm wide; lower surface of costae and costules rather persistently hairy. |
| 4 | Ultimate branches 30-55 cm long, 5-7 cm wide; costae at first with many shining hairs (1-1.5 mm long) throughout |
| 4' | Ultimate branches 15-25 cm long, 2.7-5 cm wide; costae with such hairs near base only. |
| 5 | At each fork, except primary and ultimate ones, one branch leafy and without accessory branch, the other branch not leafy and with an accessory branch |
| 5' | At each fork, except (in most cases) an ultimate one, a pair of accessory branches present. |
