- ≡ Trichomanes lyallii (Hook.f.) Hook. ex Hook. & Baker, Syn. Fil. [Hooker & Baker] 77 (1867)
- ≡ Sphaerocionium lyallii (Hook.f.) Copel., Philipp. J. Sci. 67: 33 (1938)
Usually epiphytic ferns, rarely terrestrial or rupestral. Rhizomes long-creeping, 0.1–0.2 mm diameter, bearing unbranched pale brown hairs up to 1.5 mm long, clustered at bases of stipes, more evenly distributed elsewhere. Fronds 9–90 mm long. Stipes 4–70 mm long, dark brown, not winged, bearing long brown bifurcate hairs. Laminae 2–4-pinnatifid or branching pseudodichotomously 2–4 times, ovate or flabellate or almost orbicular, 4–40 mm long, 6–34 mm wide, pale green, membranous, with marginal teeth bearing long bifurcate hairs, and sparse bifurcate hairs on costae. Rachises winged, dark brown, bearing sparse bifurcate hairs. Primary pinnae in 2–5 pairs, not overlapping, winged throughout, obovate or flabellate, all adnate; distal portion of primary pinnae straight; the longest primary pinnae at the base, 6–21 mm long, 3–13 mm wide. Secondary pinnae arising basiscopically or both basiscopically and acroscopically, not overlapping, obovate, winged throughout, adnate; the longest secondary pinnae 2–18 mm long, 2–10 mm wide. Ultimate lamina segments oblong, up to 6 mm long, 1.1–2.4 mm wide; apices obtuse or truncate or emarginate; margins with minute teeth, lacking a distinct border; distal segments on primary pinnae divergent. Sori terminating ultimate segments throughout primary pinnae, solitary, many on each primary pinna, immersed in lamina; indusia bivalvate; indusial flaps obovate or obtriangular or broader than long, 1–2 mm long, apices obtuse or truncate, margins entire, hairy on margins; receptacles included within indusial flaps.
Hymenophyllum lyallii is distinguished by its flabellate fronds with minute marginal teeth bearing bifurcate hairs. No other New Zealand species of filmy fern has flabellate fronds or bifurcate hairs, although stellate hairs are present in H. frankliniae and H. malingii. However, sterile fronds of H. lyallii are often confused with a group of common liverworts, including Hymenophyton flabellatum and Symphyogyna species.
North Island: Northland, Auckland, Volcanic Plateau, Taranaki, Southern North Island.
South Island: Western Nelson, Sounds-Nelson, Westland, Southland, Fiordland.
Chatham Islands, Stewart Island, Auckland Islands.
Altitudinal range: 0–925 m.
Hymenophyllum lyallii occurs in lowland and montane areas of the North Island from Doubtless Bay to Rotorua and Mt Taranaki, with an outlying population on Mt Arawaru, Tararua Ranges. There is also an unlocalised collection in the Cheeseman Herbarium made by Colenso from the Ruahine Ranges (AK 142002). The species has only rarely been recorded below 250 m but reaches 850 m on Mt Kaitarakihi and Mt Pirongia, and 925 m on Mt Te Aroha. In the South Island, it occurs in lowland and montane areas of the west coast from Nelson to Fiordland, western Southland and Stewart Island. It ranges from sea level up to 1000 m in the Bryant Range, north-west Nelson and Mt Davy, Paparoa Range. It is known from a single collection each on the Chatham Islands (AK 305162, WELT P023356) and Auckland Islands (CHR 323171).
Also Australia (New South Wales).
Occurs in kauri, podocarp, beech and broadleaved forest, usually as an epiphyte or at the base of trunks, but also on old stumps, mossy banks, rock faces and under overhangs. It has been recorded growing on Cyathea dealbata, C. smithii, Dicksonia squarrosa, Dacrydium cupressinum, Lepidothamnus intermedius, Libocedrus bidwillii, Lophozonia menziesii, Metrosideros sp., Quintinia serrata and Weinmannia racemosa.
n = 36 (Brownlie 1965).
Hymenophyllum lyallii has been recorded for New Caledonia by Ebihara et al. (2004). However, DNA sequencing suggests that New Caledonian plants are not closely related to Australian and New Zealand plants and may belong to a different species (Perrie et al. 2016).