Nomenclature
Scientific Name:
Hymenophyllum Sm., Mém. Acad. Roy. Sci. (Turin) 5: 418 (1793)
Synonymy:
  • = Cardiomanes C.Presl, Hymenophyllaceae 12 (1843)
Etymology:
From the Greek hymeno- (membranous), and -phyllus (leaved), a reference to the membranous fronds.
Vernacular Name(s):
filmy fern; mauku
 Description
Epiphytic, terrestrial or rupestral ferns. Rhizomes long-creeping or erect, usually filiform or wiry, nearly glabrous or bearing sparse multicellular hairs or occasionally densely hairy; roots few and fine. Fronds monomorphic. Laminae undivided to 5-pinnatifid, or flabellate, digitate (not NZ) or dichotomously divided, membranous and usually one cell thick or rarely 2–4 cells thick, often translucent, glabrous or hairy; margins entire or toothed, differentiated marginal cells sometimes forming a distinct border. Veins free. Sori terminating veins at margins of lamina. Indusia usually bivalvate or rarely urceolate, not widened at the mouth; receptacles usually included within indusial flaps, or rarely short-exserted. Spores trilete, radially symmetrical, papillate to echinate.
 Taxonomy
A genus of c. 330 species (Iwatsuki in Kramer & Green 1990) as defined by Ebihara et al. (2006).

The genus Hymenophyllum was re-defined by Ebihara et al. (2006) to include a number of taxa previously thought to belong in Trichomanes sens. lat. (notably Cardiomanes, Microtrichomanes and Pleuromanes). The Pacific species of the genus Hymenophyllum have been enumerated by Ebihara & Iwatsuki (2007) and Ebihara et al. (2010).

New Zealand species are assigned to the following subgenera:-

Subgenus Hymenophyllum: H. armstrongii, H. bivalve, H. cupressiforme, H. minimum, H. multifidum, H. peltatum, H. revolutum (7 species).

Subgenus Sphaerocionium: H. frankliniae, H. lyallii, H. malingii (3 species).

Subgenus Mecodium: H. polyanthos, H. rarum (2 species).

Subgenus Globosa: H. australe, H. demissum, H. flexuosum, H. pluviatile (4 species).

Subgenus Pleuromanes: H. flabellatum, H. rufescens (2 species).

Subgenus Myrmecostylum: H. sanguinolentum, H. scabrum, H. villosum (3 species).

Subgenus Fuciformia: H. pulcherrimum (1 species).

Subgenus Diploophyllum: H. dilatatum (1 species).

Subgenus Cardiomanes: H. nephrophyllum (1 species).
 Key
1Margins of ultimate lamina segments prominently toothed or spiny2
Margins of ultimate lamina segments entire9
2Margins of ultimate lamina segments bearing branched hairslyallii
Margins of ultimate lamina segments lacking hairs3
3Laminae undivided or forked or 1-pinnatifid, usually <20 mm long (range 3–28 mm)4
Laminae at least 2-pinnatifid, usually >20 mm long (range 7–280 mm)5
4Sori stalked, terminating rachises; indusial flaps toothed, spiny on the outer surfacesminimum
Sori lacking stalks, terminating lamina segments; indusial flaps entire, lacking spinesarmstrongii
5Laminae 7–120 mm long, 5–30 mm wide, 1–3-pinnatifid, more or less flat; 1–3 sori on each primary pinna6
Laminae 10–280 mm long, 7–165 mm wide, usually 4–5-pinnatifid (rarely 3-pinnatifid), often with the margins curved downwards; 1–several sori on each primary pinna8
6Rachises winged only in distal half; indusial flaps deeply toothedrevolutum
Rachises winged throughout; indusial flaps entire or only slightly toothed7
7Secondary pinnae arising on both sides of primary pinnae; 1 sorus on each primary pinna; indusial flaps slightly toothedcupressiforme
Secondary pinnae arising only on acroscopic side of primary pinnae; 1–3 sori on each primary pinna; indusial flaps entirepeltatum
8Sori occurring only close to the rachis, bent up at 90º to plane of frond; indusial flaps fused for half their length into a tube; receptacles usually exserted (up to 6 mm); rachis wings toothedmultifidum
Sori occurring throughout the length of the pinna, not bent upwards; indusial flaps free almost to base; receptacles not or rarely exserted; rachis wings entire or very shallowly toothedbivalve
9Rhizomes, stipes and/or laminae distinctly hairy10
Rhizomes, stipes and laminae glabrous, or bearing only very scattered hairs17
10Hairs more or less absent from lamina surfaces11
Hairs present on lamina surfaces13
11Indusial flaps with distinct crests on their outer surfaces; fronds strongly aromatic, staining paper yellow or brown when driedsanguinolentum
Indusial flaps lacking crests; fronds rarely aromatic, or staining paper when dried12
12Stiff bristly hairs densely covering stipe and lower rachis; laminae olive-green; pinnae ovate, never flabellatescabrum
Tufts of long yellowish hairs on rhizomes, stipes and rachises; laminae yellow-green; pinnae often flabellateflabellatum
13Lamina hairs mostly confined to margins; laminae flabellate, segments forkinglyallii
Lamina hairs either absent from margins, or on surfaces and margins; laminae ovate, elliptic or triangular, 1–5-pinnatifid14
14Lamina hairs stellately branched15
Lamina hairs unbranched, or only rarely branched16
15Hairs grey on adaxial lamina surface, reddish brown on abaxial surface; ultimate lamina segments round in cross-section; ferns confined to Libocedrus or sometimes Metrosideros and Halocarpus trunksmalingii
Hairs tawny or rusty-brown on both lamina surfaces; ultimate lamina segments flattened; common on tree fern and other trunksfrankliniae
16Laminae triangular, 8–55 mm long, usually shorter than stipes, 1–3-pinnatifid, densely covered in long, woolly hairsrufescens
Laminae ovate or elliptic, 20–200 mm long, longer than stipes, 3–5-pinnatifid, variably covered in short, slightly curled hairsvillosum
17Laminae undivided, reniformnephrophyllum
Laminae 1–5 pinnatifid, generally ovate or elliptic, never reniform18
18Stipes not winged, or only slightly winged distally19
Stipes winged for at least half their length, sometimes very narrowly20
19Laminae 2–3-pinnatifid, 10–200 mm long, 8–40 mm wide; sori sunk in apices of ultimate lamina segments, solitaryrarum
Laminae 3–5-pinnatifid, 45–270 mm long, 22–160 mm wide; sori free on apices of short ultimate segments, often paireddemissum
20Rhizomes erect or short-creepingpulcherrimum
Rhizomes long-creeping21
21Wings on stipe and rachis flexuous throughoutflexuosum
Wings on stipe and rachis planate, or only slightly or partly flexuose22
22Indusial flaps with distinct crests on their outer surfaces; fronds strongly aromatic, staining paper yellow or brown when driedsanguinolentum
Indusial flaps lacking crests; fronds rarely aromatic, or staining paper when dried23
23Sori partially immersed in lamina segments; indusial flaps elliptic, orbicular or obovate24
Sori adnate to lamina segments; indusial flaps usually triangular or ovate, rarely elliptic or orbicular25
24Ultimate lamina segments 0.8–1.2 mm wide, apices obtuse, truncate or emarginate; indusial flaps elliptic to obovate; plants confined to Raoul Islandpolyanthos
Ultimate lamina segments 1.3–2.5 mm wide, apices acute or obtuse but never emarginate; indusial flaps elliptic to orbicular; plants widespreaddilatatum
25Laminae 4–5-pinnatifid; lamina segments divaricate, not curved towards frond apex; apices of segments rounded or shallowly emarginate; stipe usually only winged in distal halfpluviatile
Laminae 2–4-pinnatifid; lamina segments in distal half curved towards frond apex; apices of segments usually strongly emarginate; stipe winged for most of its lengthaustrale
 Recognition
Hymenophyllum is characterised morphologically by its bivalvate indusia and receptacles that are usually included within the valves. However, three New Zealand species, H. minimum, H. multifidum and H. nephrophyllum, often have receptacles that are exserted for a short distance beyond the indusium, and in several other species the receptacles are occasionally slightly exserted. In H. nephrophyllum the indusia are also urceolate. The rhizomes in species of Hymenophyllum are generally almost glabrous or bear only scattered hairs near the stipe bases, in contrast to those in Trichomanes which are abundantly covered in red-brown hairs.

Most New Zealand species of Hymenophyllum have lamina segments that are a single cell thick, except for the costae. A few species have a differentiated margin which may be more than one cell thick, and three species, H. dilatatum, H. nephrophyllum and H. scabrum, have laminae that are 2–4 cells thick throughout. However, these characters are not especially useful in identification of individual species.
 Distribution
Distributed throughout the tropics and south temperate regions, with a few species extending also into north temperate regions. Nine of the ten subgenera of Hymenophyllum recognised by Ebihara et al. (2006) occur in the Pacific region, and 63 of c. 330 species are represented there. All of those nine subgenera also occur in New Zealand. Diploophyllum and Cardiomanes are endemic to New Zealand, and the region is probably the centre of diversity of subgenus Pleuromanes (Ebihara et al. 2010). 24 species in New Zealand; 14 endemic.
 Biostatus
Indigenous (Non-endemic)
Number of species in New Zealand within Hymenophyllum Sm.
CategoryNumber
Indigenous (Endemic)14
Indigenous (Non-endemic)10
Total24
 Cytology
Base chromosome numbers of x = 11 to 36 are recorded for Hymenophyllum (Ebihara et al. 2006).
 Notes
The following species were excluded from the New Zealand flora by Brownsey et al. (1985): Hymenophyllum ciliatum (Sw.) Sw., Hymenophyllum emarginatum Sw., Hymenophyllum secundum Hook. et Grev. and Hymenophyllum tortuosum Hook. & Grev.
 Bibliography
Brownsey, P.J.; Given, D.R.; Lovis, J.D. 1985: A revised classification of New Zealand pteridophytes with a synonymic checklist of species. New Zealand Journal of Botany 23(3): 431–489.
Brownsey, P.J.; Perrie, L.R. 2016: Hymenophyllaceae. In: Breitwieser, I; Heenan, P.B.; Wilton, A.D. Flora of New Zealand — Ferns and Lycophytes. Fascicle 16. Manaaki Whenua Press, Lincoln.
Brownsey, P.J.; Smith-Dodsworth, J.C. 2000: New Zealand ferns and allied plants. Edition 2. David Bateman, Auckland.
Ebihara, A.; Dubuisson, J.-Y.; Iwatsuki, K.; Hennequin, S.; Ito, M. 2006: A taxonomic revision of Hymenophyllaceae. Blumea 51: 221–280.
Ebihara, A.; Iwatsuki, K. 2007: The Hymenophyllaceae of the Pacific area. 1. Hymenophyllum subgenus Hymenophyllum. Bulletin of the National Science Museum, series B (Botany) 33: 55–68.
Ebihara, A.; Nitta, J.H.; Iwatsuki, K. 2010: The Hymenophyllaceae of the Pacific area. 2. Hymenophyllum (excluding subgen. Hymenophyllum). Bulletin of the National Science Museum, series B (Botany) 36: 43–59.
Kramer, K.U.; Green, P.S. 1990: Pteridophytes and gymnosperms. Kubitzki, K. (ed.) The Families and Genera of Vascular Plants. Vol. 1. Springer-Verlag, Berlin.
Large, M.F.; Braggins, J.E. 1991: Spore atlas of New Zealand ferns and fern allies. SIR Publishing, Wellington.
Presl, C.B. 1843: Hymenophyllaceae. Haase, Prague.
Smith, J.E. 1793: Tentamen botanicum de filicum generibus dorsiferarum. Mémoires de l'Académie Royale des Sciences de Turin 5: 401–422.