| 1 | Stipe and rachis bearing ± copious dark spines (bases of former scales); sori in most cases exindusiate. |
| 1' | Stipe (except base) and rachis smooth; scales, if present, not spine-like; sori in almost all species indusiate. |
| 2 | Pinnae not over 4.5 cm wide; costules not over 5 mm apart. |
| 2' | Largest pinnae 7-12 cm wide with costules 10-12 mm apart. |
| 3 | Pinnae to 4.5 cm long; pinna-lobes concave beneath; stipe-scales to 4 mm long. |
| 3' | Pinnae larger; pinna-lobes not concave beneath; stipe-scales 8 mm or more long. |
| 4 | Sori exindusiate. |
| 4' | Sori indusiate |
| 5 | Sporangia bearing several long setae |
| 5' | Sporangia lacking setae. |
| 6 | Pinnae to 9x 1.2 cm; basal veins both passing to margin above base of sinus |
| 6' | Pinnae of well-grown plants much larger; basal veins both ending beside sinus-membrane. |
| 7 | Stipe-scales terete at base and apex, less than 0.5 mm wide in middle; pinnae to 4.5 cm wide |
| 7' | Stipe-scales flat except at base, largest at least 1mm wide; pinnae rarely more than 3 cm wide |
| 8 | All pinna-lobes or pinnules auricled at base on basiscopic side; veins forked or pinnate in the auricles |
| 8' | Pinna-lobes not thus auricled. |
| 9 | Pinnae lobed almost to costae; lobes not separately adnate |
| 9' | Pinna-lobes in basal half of pinnae separately adnate to costa |
| 10 | Pinnae 1-5 pairs; apical lamina pinna-like; costules 5-7 mm apart |
| 10' | Pinnae commonly to at least 10 pairs, or if fewer costules 3-4 mm apart. |
| 11 | No indusia; no setae on sporangia. |
| 11' | Indusia present, or if absent all sporangia setiferous. |
| 12 | Aerophores elongate; sori near costules |
| 12' | Aerophores not elongate; sori medial |
| 13 | Sporangia all setiferous; no glands present. |
| 13' | Sporangia usually with glands; setae, if present, short and not on all sporangia, sometimes alternating with glands. |
| 14 | Sori supramedial; sporangia with 1-3 short setae |
| 14' | Sori medial or inframedial; sporangia bearing several long setae. |
| 15 | Veins 10-12 pairs; largest pinnae not over 12 X 2.5 cm, almost sessile. |
| 15' | Veins 14-16 pairs; largest pinnae 21 x 3.3 cm, with stalks 3-4 mm long. |
| 16 | Sori supramedial. |
| 16' | Sori medial or inframedial. |
| 17 | Pinnae to 20 x 3 cm; veins 15-18 pairs. |
| 17' | Pinnae smaller; veins not over 12 pairs. |
| 18 | Indusia overlapping margin; basal acroscopic lobe of lower pinnae elongate with forked veins |
| 18' | Indusia not overlapping margin; basal acroscopic lobe of lower pinnae not enlarged |
| 19 | Both basal lobes on basal pinnae free and short-stalked |
| 19' | Basal lobes of basal pinnae not free |
| 20 | Pinna-lobes on both sides of costa conspicuously falcate. |
| 20' | Pinna-lobes not conspicuously falcate on both sides of costa. |
| 21 | Upper surface glabrous between veins; pinnae 8 pairs |
| 21' | Upper surface bearing hairs between veins; pinnae 20 pairs. |
| 22 | Hairs on lower surface of rachis and costae 1 mm long, on upper surface between veins appressed |
| 22' | Hairs on lower surface of rachis and costae 0.3 mm long, on upper surface between veins short-erect |
| 23 | Basal 10-12 pairs of pinna-lobes separately adnate to costa |
| 23' | At most 1 free pinna-lobe separately adnate. |
| 24 | Pinnae to 25 x 5 cm, all except distal ones stalked; lower pinnae with stalks 3-6 mm; indusia small, caducous |
| 24' | Pinnae smaller; most pinnae almost sessile, basal ones with stalks at most 2-3 mm long; indusia firm, persistent. |
| 25 | Veins 20 pairs or more. |
| 25' | Veins 10-15 pairs. |
| 26 | Basiscopic lobes of all pinnae strongly falcate and shorter than acroscopic lobes; basal scales to 20 mm long, very narrow |
| 26' | Basiscopic lobes, if falcate, not or little shorter than acroscopic; basal scales much shorter, usually wider. |
| 27 | Basal acroscopic lobe of basal pinnae free, wider than the rest, with some forked veins |
| 27' | Basal acroscopic lobe of basal pinnae otherwise. |
| 28 | Lower surface quite glabrous. |
| 28' | Lower surface of costules at least bearing acicular hairs. |
| 29 | Pinnae c. 11x2 cm; basal acroscopic lobe of basal pinnae reduced. |
| 29' | Pinnae c. 22 x 3 cm; basal acroscopic lobe of basal pinnae elongate. |
| 30 | Pinnae lobed to 0.5 mm from costa |
| 30' | Pinnae lobed to 1-2 mm from costa. |
| 31 | Basal pinnae with stalks 2 mm or more long. |
| 31' | Basal pinnae sessile or nearly so. |
| 32 | Pinnae lobed to 1.5-2 mm from costa |
| 32' | Pinnae lobed to less than 1 mm from costa. |
| 33 | Basal scales thick, narrow; sori a little inframedial |
| 33' | Basal scales c. 5 x 1.5 mm; sori near costules |
| 34 | Pinnae to 6 cm long; lobes on basiscopic side strongly falcate, on acroscopic side almost straight |
| 34' | Pinnae longer; lobes on basiscopic side not greatly different from those on acroscopic side. |
| 35 | Aerophores small, dark; sori medial or a little inframedial. |
| 35' | Aerophores pale, slender, 1 mm long; sori near costules |
| 36 | Some sporangia bearing setae |
| 36' | Sporangia lacking setae, glands usually present |
