Hymenophyllum pluviatile Perrie & Brownsey

Terrestrial, rupestral or occasionally epiphytic ferns. Rhizomes long-creeping, 0.5–1 mm diameter, glabrous or bearing pale brown hairs up to 1 mm long clustered at bases of stipes. Fronds 75–190 mm long. Stipes 30–90 mm long, reddish brown, very narrowly winged in distal half, glabrous or bearing a few scattered hairs at base; stipe wing planate. Laminae 4–5-pinnatifid, elliptic or ovate or rarely triangular, 40–130 mm long, 20–70 mm wide, green, membranous, glabrous. Rachises winged throughout, reddish brown, glabrous; rachis wing planate or slightly flexuous. Primary pinnae in 5–15 pairs, scarcely overlapping, winged throughout; distal portion of primary pinnae straight; distal primary pinnae narrowly ovate or ovate, adnate; proximal primary pinnae ovate, adnate; the longest primary pinnae at or below the middle, 11–55 mm long, 11–25 mm wide. Secondary pinnae arising both acroscopically and basiscopically, scarcely overlapping, winged throughout, adnate; ovate or elliptic on distal primary pinnae, ovate or elliptic on proximal primary pinnae; the longest secondary pinnae 7–17 mm long, 4–11 mm wide. Ultimate lamina segments oblong, up to 5 mm long, 0.5–1.2 mm wide, planate or slightly flexuous; apices obtuse or truncate or occasionally emarginate; margins entire, lacking a distinct border; distal segments on primary pinnae divergent. Sori borne on short acroscopic and basiscopic segments throughout pinnae, solitary or sometimes paired, many on each primary pinna, adnate; indusia bivalvate; indusial flaps ovate or elliptic or almost orbicular, 0.75–1.5 mm long, apices acute, obtuse or truncate, margins almost entire or irregularly dentate; receptacles included within indusial flaps.

Hymenophyllum pluviatile is a small to medium-sized filmy fern distinguished by its ovate or triangular frond and narrow planate wings on the stipe. It can be distinguished from other species with winged stipes by its creeping rhizome (cf. erect rhizome in H. pulcherrimum), indusium flaps lacking crests (cf. crested indusial flaps in H. sanguinolentum), narrow planate stipe wings (cf. broad, usually flexuous wings in H. flexuosum), and smaller laminae (40–130 mm long, 20–70 mm wide cf. 60–430 mm long, 40–170 mm wide in H. dilatatum and H. flexuosum).

Hymenophyllum pluviatile is most easily confused with H. australe but can be distinguished by its epiphytic, rupestral or terrestrial habitat (cf. confined to rock in and near streams), its more divided frond (4–5-pinnatifid, cf. 2–4-pinnatifid), stipe wings which are very narrow and largely confined to the distal half, primary pinnae which tend to be straight rather than curved acroscopically, and ultimate lamina segments which are divergent rather than curved towards the frond apex, and are obtuse or truncate rather than emarginate.

Hymenophyllum pluviatile grows on rock, on soil banks, or as a low epiphyte on mossy tree trunks in wet, shaded beech, podocarp or broadleaved forest in areas with rainfall exceeding 1000 mm per year, and usually more than 1500 mm. It has been recorded as an epiphyte on Dacrydium cupressinum, Podocarpus sp., Prumnopitys ferruginea, Beilschmiedia tawa, Metrosideros umbellata and Myrsine sp.