Filmy ferns add a delicate, enveloping beauty to New Zealand’s forests. Most are translucent, with fronds only one or a few cells thick. Most are small, but they can carpet large areas of the ground or be prominent on the trunks of trees.
Irirangi or Hymenophyllum demissum is an especially common filmy fern in New Zealand. While many species grow epiphytically (on trees), irirangi often grows on the ground. It can be distinguished by its narrow (or elongated) oval reproductive structures that are often in pairs. Photo © Leon Perrie.
New Zealand is home to 31 species of filmy ferns. That’s nearly one-sixth of New Zealand’s indigenous ferns and lycophytes, and the Hymenophyllaceae has more species than any other fern family in New Zealand. Seventeen of these 31 species are only found in New Zealand. The remainder are shared with Australia, the Pacific, or further afield. Worldwide, there are some 600 species in the Hymenophyllaceae family.
We’ve just published the chapter on the Hymenophyllaceae filmy ferns for the electronic Flora of New Zealand (eFloraNZ), which covers pretty much everything you might want to know about the diversity and distribution of these ferns.
As with all eFloraNZ chapters, the filmy fern chapter come in two forms:
- the web version. With its hyperlinks, this is good for browsing through. And it has bigger pictures.
- the pdf version. (22 MB.) This is good if you prefer a more book-like experience. You can print the pdf, and go offline.
Hymenophyllum and Trichomanes
Two filmy fern genera are recognised in New Zealand. Twenty-four of New Zealand’s species belong to Hymenophyllum, with the other seven species in Trichomanes
Most Hymenophyllum species have their spore capsules enclosed by two flaps. This is Hymenophyllum revolutum. Photo © Leon Perrie.
In Trichomanes, the spore capsules are surrounded by a tube. This is Trichomanes venosum. Photo Leon Perrie. © Te Papa.
The distinctive kidney fern or Hymenophyllum nephrophyllum is unusual within Hymenophyllum in that the spore capsules sit within a tube. Indeed, it used to be classified in Trichomanes, as T. reniforme. However, analyses of DNA sequences have shown kidney fern to be more closely related to Hymenophyllum than Trichomanes. It is nevertheless evolutionarily isolated within Hymenophyllum. Photo © Leon Perrie.
New Zealand is a special place for the Hymenophyllum filmy ferns. Nine of the world’s ten subgenera occur in New Zealand. Nowhere else has as many. (And two of the subgenera are found only in New Zealand.)
The eFloraNZ chapter includes a distribution map for each species. These are based on herbarium specimens held by Te Papa, Auckland Museum, and Landcare Research (and supplemented by records from Otago University).
The eFloraNZ map for Hymenophyllum rarum. © Landcare Research 2016 CC-BY 3.0 NZ.
Distribution maps are fascinatingly revealing about the species in question as well as New Zealand’s physical environment (and the behaviour of botanical collectors). The maps for most filmy ferns show a strong bias for the wetter west, especially in the South Island, albeit often with outposts around Banks Peninsula and Dunedin.
Some common New Zealand species
As an introduction to the diversity of New Zealand’s filmy ferns, here are a few of the more common species.
Piripiri or Hymenophyllum sanguinolentum is a common epiphyte in lowland forests. It is distinguished by the crests on the back of the flaps that enclose the spore capsules. The species name of sanguinolentum refers to the blood smell of its dried fronds. Photo Leon Perrie. © Te Papa.
Hymenophyllum villosum is an upland relative of H. sanguinolentum, and differs in being hairy and lacking the soral crests. Both species curl their fronds during drought, but (slowly) unfurl on rehydration (give it a go when you next see a curled filmy fern). Photo Leon Perrie. © Te Papa.
Not all filmy ferns are translucent. The fronds of Hymenophyllum frankliniae are covered in hairs. Photo Leon Perrie. © Te Papa.
Filmy ferns may look delicate, but some are impressively hardy. Hymenophyllum multifidum ranges from sea-level up to elevations of 1800 m, within the alpine zone. It is also one of the few filmy fern species that occurs with any regularity in New Zealand’s drier east. Hymenophyllum multifidum is recognised by the reproductive structures being bent upwards at about 90 degrees from the plane of the frond, as well as the ‘teeth’ on the margins of the frond segments. Photo Leon Perrie. © Te Papa.
Trichomanes venosum is the most common species of its genus in New Zealand. It usually occurs on tree fern trunks. It is recognised by the many veins in each frond segment. Photo © Leon Perrie.
If you would like to know the names of the filmy ferns that you see, the eFloraNZ includes an identification key. Alternatively, take a photo of a filmy fern and upload it to the citizen science website NatureWatchNZ. The features to take particular note of, especially with Hymenophyllum, are: the shape and position of the reproductive structures; the presence of hairs; and whether there are ‘teeth’ on the margins of the frond segments.
Some overseas species for comparison
Since New Zealand has only a few species of Trichomanes, here are a few overseas species to stretch the imagination.
Trichomanes javanicum (or a relative). Solomon Islands. Photo Leon Perrie. © Te Papa.
Trichomanes laetum, which is little more than a collection of branched bristles. New Caledonia. Photo Leon Perrie. © Te Papa.
Trichomanes maximum, showing that some filmy ferns can get quite big. New Caledonia. Photo Leon Perrie. © Te Papa.
Trichomanes tahitense, comprising circular fronds strung along a rhizome, and recognisable as a fern really only by its reproductive structures. Vanuatu. Photo © Leon Perrie.