Hymenophyllum Sm.

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.

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).

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.

Base chromosome numbers of x = 11 to 36 are recorded for Hymenophyllum (Ebihara et al. 2006).

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.