Classification
 Nomenclature
Scientific Name:
Hymenophyllum pluviatile Perrie & Brownsey in Perrie et al., New Zealand J. Bot. 51: 317 (2013)
Synonymy:
Holotype: New Zealand, South Island, near Franz Josef, L.R. Perrie 6728 et al., 30 May 2012, WELT P024270 (mounted on sheets A and B). Isotype: CHR.
Etymology:
From the Latin pluviatile (of or pertaining to rain), a reference to the distribution of this species in areas of high rainfall.
 Description

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.

 Recognition

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.

 Distribution

North Island: Northland, Auckland, Volcanic Plateau.

South Island: Western Nelson, Westland, Fiordland.

Altitudinal range: 20–800 m.

Hymenophyllum pluviatile is confined to areas of high rainfall on the west coast of both islands, apart from one collection from Tauhara near Taupō. It extends from Waimā Forest in Northland to Doubtful Sound in Fiordland, and a more southerly but imprecisely located 1918 collection "on track to Preservation Inlet" (AK 139880). In the North Island it grows mostly above 400 m, reaching 800 m on Mt Pirongia, and possibly up to 1000 m on Tauhara. In the South Island it extends from 20 m in Fiordland to over 600 m on Mt Burnett, north-west Nelson. It has been observed on Stewart Island (see NatureWatchNZ 1467047), but not yet collected from there, and hence not recorded on the distribution map.

 Habitat

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.

 Biostatus
Indigenous (Endemic)

Hymenophyllum pluviatile was given a conservation status of Nationally Vulnerable (as the taxonomically indeterminate H. aff. flexuosum) by de Lange et al. (2013).

 Bibliography
Brownsey, P.J.; Perrie, L.R. 2016: Hymenophyllaceae. In: Breitwieser, I; Heenan, P.B.; Wilton, A.D. (ed.) Flora of New Zealand — Ferns and Lycophytes. Fascicle 16. Manaaki Whenua Press, Lincoln.
de Lange, P.J.; Rolfe, J.R.; Barkla J.W.; Courtney, S.P.; Champion, P.D.; Perrie, L.R.; Beadel, S.N.; Ford, K.A.; Breitwieser, I.; Schönberger, I.; Hindmarsh-Walls, R.; Heenan, P.B.; Ladley, K. 2018: Conservation status of New Zealand indigenous vascular plants, 2017. New Zealand Threat Classification Series. No. 22. [Naturally Uncommon]
de Lange, P.J.; Rolfe, J.R.; Champion, P.D.; Courtney, S.P.; Heenan, P.B.; Barkla, J.W.; Cameron, E.K.; Norton, D.A.; Hitchmough, R.A. 2013: Conservation status of New Zealand indigenous vascular plants, 2012. New Zealand Threat Classification Series 3. Department of Conservation, Wellington.
Perrie, L.R.; Shepherd, L.D.; de Lange, P.J.; Batty, E.L.; Ohlsen, D.J.; Bayly, M.J.; Brownsey, P.J. 2013: Hymenophyllum pluviatile, a new and uncommon fern from New Zealand. New Zealand Journal of Botany 51(4): 308–320.