1Veins anastomosing.
1'Veins free.
2Stipe and rachis bearing many dark spines 1 mm long irregularly arranged.
2'Stipe and rachis lacking such spines.
3Indusia lacking.
3'Indusia present.
4Pinnae 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.
5Pinnae short-acuminate (Sumatra)
5'Pinnae narrowly long-acuminate (Philippines)
6Elongate aerophores present at bases of pinnae.
6'Aerophores not elongate (in many cases slightly swollen).
7Reduced pinnae consisting of a prominent aerophore with a minute rim.
7'Reduced pinnae with a distinct lamina.
8Pinnae crenate; veins 6-7 pairs
8'Pinnae lobed ⅓ towards costa; veins 10-16 pairs
9Indusia lacking.
9'Indusia present.
10Pinnae 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
11Veins 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.
12Lower pinnae gradually reduced; stipe 5-15 cm long.
12'Abrupt transition to reduced pinnae; stipe 20 to 50 cm long
13Basal pinnae auricled on acroscopic base.
13'Basal pinnae not auricled on acroscopic base.
14Basal large pinnae narrowly cuneate at base on basiscopic side.
14'Basal pinnae truncate at base on basiscopic side.
15Brown hairs on rachis both sides; pinnae to 8 cm long
15'Lower surface of rachis glabrous; pinnae 3-3.5 cm long.
16Pinnae lobed 2/5-½ towards costa
16'Pinnae crenate
17Basal 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.
18Basal pinnae not or variably a little reduced.
18'At least 1 pair basal pinnae conspicuously reduced.
19Pinnae 4 cm or more wide, lobed less than ½
19'Pinnae to 2.5 cm wide, lobed more than ½
20Middle and upper pinnae very oblique, their bases asymmetric; apices of pinnae long and very narrow.
20'Middle pinnae not very oblique, their bases ± symmetrical.
21Largest reduced pinnae and lower normal ones distinctly auricled at their bases
21'Lower pinnae narrowed towards their bases and not auricled.
22Pinnae 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
23One pair basal pinnae reduced.
23'At least 2 pairs of abruptly reduced pinnae or several pairs gradually reduced.
24Reduced pinnae 2 cm long; normal pinnae lobed more than ½.
24'Reduced pinnae 1 mm long; normal pinnae lobed less than ½.
25Reduced pinnae and lower normal pinnae with large serrate or lobed acroscopic auricles.
25'Reduced pinnae and lower normal pinnae not thus auricled.
26Reduced pinnae 2-4 pairs, subequal
26'Reduced pinnae to 8 pairs, decreasing downwards
27Hairs 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.
28Pinnae lobed less than ½; h pairs of veins anastomosing
28'Pinnae lobed ½-⅔; basal veins meeting at base of sinus-membrane.
29Lower pinnae gradually decrescent, at least on fertile fronds.
29'Transition from normal to reduced pinnae abrupt.
30Indusia very small; lower surface bearing minute glands between veins.
30'Indusia conspicuous; lower surface lacking such glands.
31Pinnae lobed ⅔ or more deeply.
31'Pinnae lobed at most 3/5 towards costa.
32Pinnae lobed to 1.5 mm from costa, not pustular between veins when dried
32'Pinnae lobed less deeply, pustular between veins.
33Pinna-lobes dentate at ends of veins
33'Pinna-lobes entire.
34Pinnae 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
35Lowest pinnae considerably narrowed towards their bases, gradually or rather abruptly.
35'Lowest pinnae not or little narrowed towards their bases.
36Pinnae of well-grown plants lobed more than ½.
36'Pinnae of well-grown plants lobed less than ½.
37Stipe-scales narrow, spreading
37'Stipe-scales thin, appressed.
38Pinnae commonly 2.5-3 cm wide; sporangia lacking glands.
38'Pinnae not over 2 cm wide; sporangia bearing glands.
39Pinnae 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.
40Pinna-lobes almost at right angles to costa; sporangia bearing glands
40'Pinna-lobes oblique; no glands on sporangia
41Upper 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
42Largest 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.
43Both surfaces of pinnae bearing short erect hairs throughout.
43'No hairs between veins on upper surface, few or none on lower.
44Lower 1-3 pairs of pinnae progressively smaller, lowest commonly 1 cm long.
44'Lower 5-6 pairs of pinnae less than 2 mm long
45Four or more pairs of lower pinnae gradually reduced; pinnae lobed c. half-way to costa
45'Not this combination of characters.
46Pinnae 2-3 cm long.
46'Pinnae much longer.
47Basal pinnae shorter than the next pair
47'Six pairs of lower pinnae ± gradually reduced.
48Basal 3-4 pairs of pinna-lobes separately adnate to costa
48'Pinnae lobed half-way to costa
49Much-reduced basal pinnae 0-3 pairs.
49'Much-reduced basal pinnae at least 6 pairs.
50Sori 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.
51Pinnae 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.
52Basal basiscopic lobes of middle pinnae equal to acroscopic lobes.
52'Basal basiscopic lobes of middle pinnae shorter than acroscopic.
53Basal acroscopic lobes of largest reduced pinnae and lowest normal pinnae elongate.
53'Basal acroscopic lobes of such pinnae reduced
54Much-reduced basal pinnae 2 pairs; hairs present on lower surface of rachis and costae
54'Much-reduced pinnae lacking; lower surfaces quite glabrous.
55Pinnae to 15 cm or more long.
55'Pinnae not or little more than 10 cm long.
56Reduced pinnae 6 pairs, lowest 1 cm long.
56'Reduced pinnae many pairs, lower ones smaller
57Pinnae lobed to 1 mm from costa.
57'Pinnae lobed to 3.5-4 mm from costa
58Sori inframedial; dark brown hairs present on upper surface of costa.
58'Sori supramedial; no dark brown hairs
59Pinnae lobed half-way to costa
59'Pinnae lobed almost to costa