| 1 | Abaxial surface of rachis bearing slender terete spine-like scales. |
| 1' | Abaxial surface of rachis in most species lacking scales; scales, if present in this position, distinctly flat. |
| 2 | Pinnae crenate to a depth of 1 mm |
| 2' | Pinnae much more deeply lobed. |
| 3 | Pinnae 8-12 pairs, 6 cm or more apart |
| 3' | Pinnae to 20 or more pairs, closer together. |
| 4 | Sori all elongate; veins not prominent on lower surface |
| 4' | At most basal sori elongate; veins rather thick and prominent beneath. |
| 5 | Pinnae not over 3 cm wide, lobed ¼-2/5; basal sori only divergent but not elongate |
| 5' | Pinnae to 3.5 cm or more wide, lobed 2/5-3/5; basal 2-3 pairs of sori divergent and lowest elongate |
| 6 | Basal veins not meeting but passing to sides of the sinus-membrane which is decurrent below their junction with it |
| 6' | Basal veins anastomosing or at least meeting below base of sinus-membrane which is not decurrent. |
| 7 | Stipe scaly throughout; at least lower part of rachis scaly on abaxial side. |
| 7' | Stipe scaly near base only; rachis not scaly on abaxial surface. |
| 8 | Pinnae to 3 cm wide, thin, drying light greenish; small indusia present. |
| 8' | Pinae not over 2.5 cm wide, firm, drying brown-olivaceous; no indusia. |
| 9 | Capitate hairs abundant on lower surface of costae and costules; capitate hairs and sessile glands between veins |
| 9' | Glands mainly sessile, lacking between veins |
| 10 | Rachis bearing slender terete scales on adaxial surface |
| 10' | Rachis lacking scales on adaxial surface, or such scales flat. |
| 11 | Pinnae crenate to a depth of 1.5-3 mm; no indusia. |
| 11' | Pinnae lobed ⅓ towards costa or more deeply; indusia present in most cases. |
| 12 | Lower surfaces covered with slender erect acicular hairs |
| 12' | Lower surfaces glabrous. |
| 13 | Pinnae thin; veins not prominent beneath; sori close to costules except lowest |
| 13' | Pinnae firm; veins prominent beneath; several pairs of lower sori gradually divergent |
| 14 | Lower surface bearing sessile glands |
| 14' | Lower surface bearing acicular and/or capitate hairs. |
| 15 | Lower surface densely acicular-hairy throughout, lacking capitate hairs; no capitate hairs on sporangia |
| 15' | Lower surface bearing short capitate hairs at least on costules and veins; capitate hairs (rarely setae) present on sporangia. |
| 16 | Pinnae thick and rigid; veins prominent on lower surface, grooved on upper surface |
| 16' | Pinnae thin; veins not prominent on lower surface nor grooved on upper surface. |
| 17 | Basal pair of veins anastomosing to form a slender excurrent vein which is joined by the second acroscopic vein before entering base of sinus-membrane. |
| 17' | Basal pair of veins meeting, or not quite meeting, at base of sinus-membrane. |
| 18 | Pinnae lobed less than half-way to costa; sori indusiate |
| 18' | Pinnae lobed more than half-way to costa; sori exindusiate |
