| 1 | All veins free in fertile fronds |
| 1' | At least costal areoles present in fertile fronds |
| 2 | Fronds very thin, appearing only in the rainy season; caudex creeping, succulent |
| 2' | Fronds not very thin, persistent; caudex not succulent |
| 3 | All pinnae very deeply lobed; free tertiary leaflets present on basal pinnae |
| 3' | Pinnae much less deeply lobed; tertiary leaflets rare |
| 4 | Bases of upper pinnae and pinnules narrowly decurrent, their basal lobes sometimes separately attached to rachis |
| 4' | Bases of upper pinnae not narrowly decurrent, their basal lobes never separately attached to the rachis |
| 5 | Basal pinnae to 22 cm long; axes glabrous on lower surface |
| 5' | Basal pinnae to 45 cm long; axes short-hairy on lower surface |
| 6 | Hairs 1 mm long present between veins on upper surface |
| 6' | Hairs on upper surface between veins few and short, mostly near sinuses |
| 7 | Basal pinnae to 12 cm long |
| 7' | Basal pinnae to 27 cm long; fronds not or little dimorphous |
| 8 | Fronds strongly dimorphous; distinct indusia present |
| 8' | Fronds not dimorphous; indusia small or lacking. |
| 9 | Basal pinnae to at least 40 cm long; suprabasal pinnae bearing 3 or 4 pairs of sessile or adnate pinnules |
| 9' | Basal pinnae not over 25 cm long; suprabasal pinnae bearing at least one pair of free pinnules |
| 10 | Sporangia bearing short capitate hairs |
| 10' | Sporangia lacking such hairs |
| 11 | Fronds dimorphous; irregular slight anastomosis of veins in sterile fronds; scales on stipe black, 10 × 1 mm |
| 11' | Fronds not or little dimorphous; no anastomosis, scales otherwise |
| 12 | Pinnae very firm, their longest lobes, if sterile, sharply dentate; no hairs near sinuses on upper surface |
| 12' | Pinnae thinner, their largest lobes not sharply dentate; some hairs present on upper surface at least near sinuses |
| 13 | Basal pinnae 7 cm long on fronds with lamina 25 cm long; very narrow black scales present on raches |
| 13' | Basal pinnae proportionately longer, with free pinnules even on smaller fronds; scales on rachis few and not black |
| 14 | Pinnae of fertile fronds much contracted as compared with those of sterile fronds |
| 14' | Pinnae of fertile fronds not or little contracted |
| 15 | Sporangia covering the lobes of fertile pinnae |
| 15' | Sporangia forming separate sori |
| 16 | Veins distinct on lower surface; rachis not dark and glossy. |
| 16' | Veins not distinct on lower surface; rachis dark and glossy. |
| 17 | Middle pinnae entire or shallowly lobed |
| 17' | Middle pinnae deeply lobed or pinnate |
| 18 | Hairs between veins on upper surface present only near sinuses |
| 18' | Hairs scattered generally between veins on upper surface |
| 19 | Free pinnules on basal pinnae at most 1 pair |
| 19' | Free pinnules on basal pinnae at least 3 pairs |
| 20 | Fronds opaque; smaller veins not distinct on lower surface. |
| 20' | Fronds not opaque, or smaller veins distinct on lower surface |
| 21 | Pinna-rachis very dark; basal pinnae not over 30 cm long; New Guinea |
| 21' | Pinna-rachis not dark; basal pinnae to 45 cm long; W Malesia. |
| 22 | Rachis and pinna-rachis densely short-hairy with very narrow dark scales on lower surface |
| 22' | Rachis and pinna-rachis neither densely short-hairy nor scaly on lower surface |
| 23 | Suprabasal pinnae almost sessile with sessile basal pinnules. |
| 23' | Suprabasal pinnae stalked with several stalked basal pinnules. |
| 24 | Sori indusiate |
| 24' | Sori exindusiate |
| 25 | No free pinnules on basal pinnae |
| 25' | At least 1 pair of free pinnules on basal pinnae |
| 26 | Anastomosis confined (or nearly so) to costal and costular areoles |
| 26' | Anastomosis comprising more than one series of small areoles below sinuses between pinna-lobes |
| 27 | Free tertiary leaflets rarely present on basal pinnae |
| 27' | Free tertiary leaflets present on fronds of mature plants |
| 28 | Hairs on lower surface of costae and costules to 0.3 mm long; veins not prominent |
| 28' | Hairs on lower surface of costae and costules to 1 mm long; veins prominent on both surfaces of dried specimens |
| 29 | Very short hairs abundant between veins on both surfaces. |
| 29' | Hairs between veins on upper surface thick, to 0.5 mm or more long, none or few on lower surface |
| 30 | Basal pinnae of mature plants bearing several pairs of free or adnate pinnules, one tertiary leaflet usually present |
| 30' | Basal pinnae of mature plants bearing one pair of pinnules; tertiary leaflets lacking |
