| 1 | Rhizome completely sclerified, scales basifixed, spores smooth |
| 1' | Rhizome with parenchymatous ground tissue, scales pseudopeltate or peltate, spores variously ornamented |
| 2 | Fronds distinctly stalked, sori spread all over the lamina |
| 2' | Fronds sessile or indistinctly stalked, sori in an apical patch |
| 3 | Phyllopods 1-2 cm apart. — Borneo |
| 3' | Phyllopods contiguous |
| 4 | Hairs with all rays appressed or approximately equally spreading |
| 4' | Hairs with appressed rays and one elongated, erect spine. — Philippines. |
| 5 | Sporangia in a longitudinal coenosorus |
| 5' | Sporangia in round or elongate, separate sori (fertile fronds absent follow this lead) |
| 6 | Rhizome scales ciliate |
| 6' | Rhizome scales entire |
| 7 | Rhizome scales elongate, over 5 times as long as wide, coenosorus sunken, paraphyses many, in a medial row in the coenosorus |
| 7' | Rhizome scales short, less than 3 times as long as wide, coenosorus superficial, paraphyses inconspicuous |
| 8 | Stellate hairs dimorphic, sterile fronds mostly not wider than the basal part of the fertile ones |
| 8' | Stellate hairs monomorphic, appressed, sterile fronds much wider than the fertile ones |
| 9 | Sori clearly in a single row between costa and margin |
| 9' | Sori in at least two rows between costa and margin (in doubt or fertile fronds absent follow this lead) |
| 10 | Small plants, fertile fronds to 0.5 cm wide, indument monomorphic, appressed. |
| 10' | Medium to large plants, fertile fronds 1 cm wide or more, indument dimorphic, loose |
| 11 | Scales brown (an aberrant form from Flores; compare also narrow forms of 19. P. rasamalae or 13. P. nummularifolia) |
| 11' | Scales with hyaline acumen |
| 12 | Sori sunken |
| 12' | Sori superficial (or fertile fronds absent) |
| 13 | Paraphyses mixed with the sporangia |
| 13' | Paraphyses in a central group in the sorus |
| 14 | Rhizome flexible, scales ciliate |
| 14' | Rhizome rigid, scales entire |
| 15 | Hydathodes absent |
| 15' | Hydathodes present |
| 16 | Stellate hairs dimorphic, not appressed |
| 16' | Stellate hairs monomorphic, appressed |
| 17 | Stellate hairs appressed, with boat-shaped straight rays |
| 17' | Stellate hairs with acicular straight rays, not appressed |
| 18 | Rhizome scales dentate or ciliate |
| 18' | Rhizome scales entire |
| 19 | Rhizome scales ciliate |
| 19' | Rhizome scales dentate |
| 20 | Sterile fronds elongate, index 3-8, apex acute, fertile fronds not much narrowed. |
| 20' | Sterile fronds ovate to rounded, index 1-2, apex rounded, fertile fronds conspicuously narrowed |
| 21 | Rhizome scales not squarrose, widest above the attachment, lamina to 62 (97) by 5.5 cm |
| 21' | Rhizome scales with long, sheathing base and squarrose acumen, widest near the attachment, lamina to 35 by 3 cm |
| 22 | Scales with hyaline acumen, often squarrosely recurved(these two species are difficult to distinguish when sterile |
| 22' | Scales brown, spreading but not recurved |
| 23 | Lamina 1.5-4 cm wide, rhizome scales 1.5-2.5 mm wide, usually widest above the attachment, sori to 2.5 mm, with many conspicuous paraphyses. |
| 23' | Lamina up to 1 cm wide, rhizome scales 0.4-1.4 mm wide, widest near the attachment, sori 1-1.5 mm, without conspicuous paraphyses. |
| 24 | Lateral buds close to the phyllopods on the other side of the rhizome. |
| 24' | Lateral buds halfway between the phyllopods |
| 25 | Rhizome without central sclerenchyma |
| 25' | Rhizome with a central sclerenchyma sheath (these two species are difficult to distinguish when sterile). 10. P. lanceolata or |
| 26 | Sori deeply sunken, rhizome elongated with lateral buds close to but opposite the phyllopods |
| 26' | Sori superficial, rhizome short or elongated with lateral buds not close to the phyllopods |
| 27 | Fronds distinctly long-stalked, the sterile fronds mostly ovate to elliptical, index 1-4 |
| 27' | Fronds not stalked, or indistinctly stalked below a very gradually decurrent lamina, sterile fronds oblanceolate, index 6-20, or absent |
| 28 | Rhizome scales dentate, stellate hairs sparse, thin, fugacious |
| 28' | Rhizome scales ciliate, stellate hairs forming a dense, persistent mat |
| 29 | Rhizome scales with appressed, straight, ciliate apex |
| 29' | Rhizome scales with spreading, entire, crisped apex |
| 30 | Rhizome short, phyllopods contiguous, rhizome scales pseudopeltate, stellate hairs monomorphic |
| 30' | Rhizome shortly elongated, phyllopods to 0.5 cm apart, rhizome scales peltate, stellate hairs dimorphic |
