| 1 | Veins anastomosing. |
| 1' | Veins free. |
| 2 | Stipe and rachis bearing many dark spines 1 mm long irregularly arranged. |
| 2' | Stipe and rachis lacking such spines. |
| 3 | Indusia lacking. |
| 3' | Indusia present. |
| 4 | Pinnae to 25 x 1.6-2.7 cm with cauda 3 cm long; spores with many small wings. |
| 4' | Pinnae to 12 x 2 cm with cauda 1.5 cm; spores with wing and cross-wings. |
| 5 | Pinnae short-acuminate (Sumatra) |
| 5' | Pinnae narrowly long-acuminate (Philippines) |
| 6 | Elongate aerophores present at bases of pinnae. |
| 6' | Aerophores not elongate (in many cases slightly swollen). |
| 7 | Reduced pinnae consisting of a prominent aerophore with a minute rim. |
| 7' | Reduced pinnae with a distinct lamina. |
| 8 | Pinnae crenate; veins 6-7 pairs |
| 8' | Pinnae lobed ⅓ towards costa; veins 10-16 pairs |
| 9 | Indusia lacking. |
| 9' | Indusia present. |
| 10 | Pinnae commonly 12-15 x 1.5-2.0 cm, thin; lower surface of rachis with or without minute acicular hairs; sporangia with capitate hairs |
| 10' | Pinnae to 7 x 1 cm, rigid when dry; lower surface of rachis densely covered with erect hairs 0.3 mm long; sporangia mostly bearing setae |
| 11 | Veins in fertile pinnae 2-5 pairs; pinnae in most cases not over 12 cm long. |
| 11' | Veins in fertile pinnae 7-10 pairs or more; pinnae usually much longer. |
| 12 | Lower pinnae gradually reduced; stipe 5-15 cm long. |
| 12' | Abrupt transition to reduced pinnae; stipe 20 to 50 cm long |
| 13 | Basal pinnae auricled on acroscopic base. |
| 13' | Basal pinnae not auricled on acroscopic base. |
| 14 | Basal large pinnae narrowly cuneate at base on basiscopic side. |
| 14' | Basal pinnae truncate at base on basiscopic side. |
| 15 | Brown hairs on rachis both sides; pinnae to 8 cm long |
| 15' | Lower surface of rachis glabrous; pinnae 3-3.5 cm long. |
| 16 | Pinnae lobed 2/5-½ towards costa |
| 16' | Pinnae crenate |
| 17 | Basal pinnae narrowly cuneate on basiscopic side; pinnae to 15 cm long including cauda 4-5 cm |
| 17' | Basal pinnae not so; pinnae, if 15 cm long, with shorter cauda. |
| 18 | Basal pinnae not or variably a little reduced. |
| 18' | At least 1 pair basal pinnae conspicuously reduced. |
| 19 | Pinnae 4 cm or more wide, lobed less than ½ |
| 19' | Pinnae to 2.5 cm wide, lobed more than ½ |
| 20 | Middle and upper pinnae very oblique, their bases asymmetric; apices of pinnae long and very narrow. |
| 20' | Middle pinnae not very oblique, their bases ± symmetrical. |
| 21 | Largest reduced pinnae and lower normal ones distinctly auricled at their bases |
| 21' | Lower pinnae narrowed towards their bases and not auricled. |
| 22 | Pinnae lobed ½ way to costa; c. 12 pairs of reduced pinnae, largest 3 cm long |
| 22' | Pinnae lobed less deeply; reduced pinnae c. 6 pairs, largest 5 mm long |
| 23 | One pair basal pinnae reduced. |
| 23' | At least 2 pairs of abruptly reduced pinnae or several pairs gradually reduced. |
| 24 | Reduced pinnae 2 cm long; normal pinnae lobed more than ½. |
| 24' | Reduced pinnae 1 mm long; normal pinnae lobed less than ½. |
| 25 | Reduced pinnae and lower normal pinnae with large serrate or lobed acroscopic auricles. |
| 25' | Reduced pinnae and lower normal pinnae not thus auricled. |
| 26 | Reduced pinnae 2-4 pairs, subequal |
| 26' | Reduced pinnae to 8 pairs, decreasing downwards |
| 27 | Hairs on upper surface of rachis thick, brown; some similar hairs usually present on lower surface of rachis and costae. |
| 27' | Hairs on rachis and costae not thick and brown. |
| 28 | Pinnae lobed less than ½; h pairs of veins anastomosing |
| 28' | Pinnae lobed ½-⅔; basal veins meeting at base of sinus-membrane. |
| 29 | Lower pinnae gradually decrescent, at least on fertile fronds. |
| 29' | Transition from normal to reduced pinnae abrupt. |
| 30 | Indusia very small; lower surface bearing minute glands between veins. |
| 30' | Indusia conspicuous; lower surface lacking such glands. |
| 31 | Pinnae lobed ⅔ or more deeply. |
| 31' | Pinnae lobed at most 3/5 towards costa. |
| 32 | Pinnae lobed to 1.5 mm from costa, not pustular between veins when dried |
| 32' | Pinnae lobed less deeply, pustular between veins. |
| 33 | Pinna-lobes dentate at ends of veins |
| 33' | Pinna-lobes entire. |
| 34 | Pinnae lobed to 2.5 mm from costa; hairs present on all parts of lower surface |
| 34' | Pinnae lobed to 4 mm from costa; lower surfaces quite glabrous |
| 35 | Lowest pinnae considerably narrowed towards their bases, gradually or rather abruptly. |
| 35' | Lowest pinnae not or little narrowed towards their bases. |
| 36 | Pinnae of well-grown plants lobed more than ½. |
| 36' | Pinnae of well-grown plants lobed less than ½. |
| 37 | Stipe-scales narrow, spreading |
| 37' | Stipe-scales thin, appressed. |
| 38 | Pinnae commonly 2.5-3 cm wide; sporangia lacking glands. |
| 38' | Pinnae not over 2 cm wide; sporangia bearing glands. |
| 39 | Pinnae commonly 20 x 2.5 cm, usually with some hairs on lower surface of costae, often also between veins |
| 39' | Pinnae not more than 2 cm wide; lower surface quite glabrous. |
| 40 | Pinna-lobes almost at right angles to costa; sporangia bearing glands |
| 40' | Pinna-lobes oblique; no glands on sporangia |
| 41 | Upper reduced pinnae longer than wide, with dilated bases and lobed distally; lower surface slightly pustular |
| 41' | Upper reduced pinnae as long as wide, not dilated at base nor lobed above base, strongly pustular between veins |
| 42 | Largest pinnae less than 2 cm long, entire or slightly crenate; many pairs of lower pinnae gradually decrescent |
| 42' | Largest pinnae in most cases larger; lower pinnae otherwise. |
| 43 | Both surfaces of pinnae bearing short erect hairs throughout. |
| 43' | No hairs between veins on upper surface, few or none on lower. |
| 44 | Lower 1-3 pairs of pinnae progressively smaller, lowest commonly 1 cm long. |
| 44' | Lower 5-6 pairs of pinnae less than 2 mm long |
| 45 | Four or more pairs of lower pinnae gradually reduced; pinnae lobed c. half-way to costa |
| 45' | Not this combination of characters. |
| 46 | Pinnae 2-3 cm long. |
| 46' | Pinnae much longer. |
| 47 | Basal pinnae shorter than the next pair |
| 47' | Six pairs of lower pinnae ± gradually reduced. |
| 48 | Basal 3-4 pairs of pinna-lobes separately adnate to costa |
| 48' | Pinnae lobed half-way to costa |
| 49 | Much-reduced basal pinnae 0-3 pairs. |
| 49' | Much-reduced basal pinnae at least 6 pairs. |
| 50 | Sori supramedial; pinnae lobed to 1-2 mm from costa; basal veins from adjacent costules often meeting, or nearly so, at the sinus. |
| 50' | Sori medial; pinnae lobed to less than 1 mm from costa; basal veins from adjacent costules ending far apart at the margin. |
| 51 | Pinnae to 23 x 4 cm; basal acroscopic lobe of middle pinnae not almost free |
| 51' | Pinnae c. 8 x 1.5 cm; basal acroscopic lobe of middle pinnae almost free. |
| 52 | Basal basiscopic lobes of middle pinnae equal to acroscopic lobes. |
| 52' | Basal basiscopic lobes of middle pinnae shorter than acroscopic. |
| 53 | Basal acroscopic lobes of largest reduced pinnae and lowest normal pinnae elongate. |
| 53' | Basal acroscopic lobes of such pinnae reduced |
| 54 | Much-reduced basal pinnae 2 pairs; hairs present on lower surface of rachis and costae |
| 54' | Much-reduced pinnae lacking; lower surfaces quite glabrous. |
| 55 | Pinnae to 15 cm or more long. |
| 55' | Pinnae not or little more than 10 cm long. |
| 56 | Reduced pinnae 6 pairs, lowest 1 cm long. |
| 56' | Reduced pinnae many pairs, lower ones smaller |
| 57 | Pinnae lobed to 1 mm from costa. |
| 57' | Pinnae lobed to 3.5-4 mm from costa |
| 58 | Sori inframedial; dark brown hairs present on upper surface of costa. |
| 58' | Sori supramedial; no dark brown hairs |
| 59 | Pinnae lobed half-way to costa |
| 59' | Pinnae lobed almost to costa |
