Fronds simple or divided, glabrous or hairy, margins entire or toothed; segments with a single vein only.
Sori marginal or terminal on the segments; involucre 2-valved, the lips ± circular or triangular; receptacle usually included within the involucre.
| | Key to the species | |
| 1 | Growing on Lord Howe Island | 2 |
| Growing on mainland | 3 |
| 2 | Fronds 5–12 cm long; ultimate pinnules 0.5–1 mm wide; margins of involucre entire | Hymenophyllum howense |
| Fronds 2–6 cm long; ultimate pinnules 1.5–2 mm wide; margins of involucre dentate
Back to 1 | Hymenophyllum moorei |
| 3 | Fronds with margins of lamina bearing simple and branched hairs | Hymenophyllum lyallii |
| Fronds with margins of lamina never bearing branched hairs
Back to 1 | 4 |
| 4 | Involucres without a definite tube at the base, or the tubular portion not immersed in the lamina | 5 |
| Involucres with a distinct obconical tube at the base, tubular portion immersed in the lamina
Back to 3 | Hymenophyllum bivalve |
| 5 | Fronds with margins of lamina toothed | 6 |
| Fronds with margins of lamina not toothed
Back to 4 | 8 |
| 6 | Sori terminal on the primary divisions of the lamina | Hymenophyllum pumilum |
| Sori borne on the margins of the primary divisions of the lamina
Back to 5 | 7 |
| 7 | Primary pinnae branching on the upper side only; margin of involucre always entire | Hymenophyllum peltatum |
| Primary pinnae branched on both sides; margin of involucre usually toothed, sometimes entire
Back to 6 | Hymenophyllum cupressiforme |
| 8 | Margins of indusia and/or lamina black and thickened; lamina simple and forked once, or rarely to 3 times | Hymenophyllum marginatum |
| Margins of lamina not black; lamina 1-pinnatifid or more divided
Back to 5 | 9 |
| 9 | Fronds with stipe and rachis distinctly winged almost to the base; sori often borne in pairs, base not immersed in the lamina | Hymenophyllum australe |
| Fronds with stipe not winged or very narrowly winged; sori never in pairs, base somewhat immersed in the lamina
Back to 8 | 10 |
| 10 | Fronds mostly at least 2–pinnate with pinnae pinnatifid; stipe and lower part of rachis unwinged | Hymenophyllum flabellatum |
| Fronds 1-pinnate or 1–2-pinnatifid; stipe unwinged or very narrowly winged
Back to 9 | Hymenophyllum rarum |
