with a stout central costa. Sori marginal, terminal or lateral, more or less immersed in the frond or quite free, always terminating a vein or costa. Indusium cup-shaped, more or less deeply 2-lipped or 2-valved, sometimes to the base, of almost the same texture as the frond, margins of the lips entire or toothed or fringed. Receptacle linear or oblong, not exserted beyond the indusium. Sporangia sessile or nearly so, depressed, surrounded by a broad complete horizontal ring, bursting transversely.
One of the most beautiful of the genera of ferns, almost wholly confined to shaded localities, and remarkable for the filmy texture of the frond, a peculiarity which it shares with Trichomanes. Species about 90, widely distributed in tropical climates and in the south temperate zone, especially abundant in New Zealand, rare in the north temperate zone. Of the 20 species found in New Zealand, 7 or perhaps 8 are endemic, the remainder are for the most part widely dispersed.
| A. Euhymenophyllum. Margin of the frond entire. | |
| * Fronds glabrous; or, if hairs are present, they are confined to the stipes, rhachis, and costæ. | |
| † Rhachis winged throughout; wing often decurrent down the stipes, sometimes to the base. | |
| Fronds 1–4 in., pendulous, flaccid, 2-pinnatifid. Stipes capillary; rhachis often wingless below. Sori large, terminal, immersed; indusium orbicular | 1. H. rarum. |
| Fronds 2–9 in., olive-green, 3-pinnatifid, sometimes with scattered hairs on the rhachis and stipes. Sori terminating short lateral segments, free; indusium broadly ovate | 2. H. polyanthos. |
| Fronds 2–6 in., brownish-green, 3–4-pinnatifid; segments narrow, crowded. Stipes, rhachis, and costae usually villous. Sori numerous, terminal, free; indusium broadly ovate | 3. H. villosum. |
| Fronds 3–9 in., triangular. Rhachis with a broad much-crisped wing decurrent almost to the base of the stipes. Sori terminal, free; indusium orbicular | 4. H. australe. |
| Fronds 2–3 in., linear-oblong, dull dark-green. Rhachis with a broad flat wing decurrent almost to the base of the stipes. Sori terminal, free; indusium ovate, margins often jagged | 5. H. atrovirens. |
| Rhizome short, bristly. Fronds 9–20 in., ovate-lanceolate, pale-green. Rhachis with a narrow flat wing decurrent down the stipes. Sori terminal, free; indusium orbicular | 6. H. pulcherrimum. |
| Rhizome long, glabrous. Fronds 9–20 in., ovate-lanceolate; segments broad, flat. Rhachis with a narrow flat wing decurrent along the stipes. Sori terminal, immersed; indusium orbicular | 7. H. dilatatum. |
| †† Rhachis winged only towards the top; lower part and stipes naked (often narrowly winged in H. demissum). | |
| Fronds 4–12 in., ovate-deltoid, bright-green; stipes and rhachis glabrous. Sori terminal, free; indusium ovate | 8. H. demissum. |
