Kidney Fern – Raurenga

Here’s a New Zealand fern that grabs your attention. It’s not world famous, but its unusual form makes the Kidney fern hard to miss. I came across a few of these ferns while exploring the Oparara Basin on the West Coast of NZ in December 2019.

Not sure if I would call them ‘beautiful’ but they are very distinctive and frankly, not especially fern-like in appearance. They lack the typical elongated or segmented frond structure you might expect to see on your average k1w1 fern.

Don’t get me wrong, I’m not saying the shiny, translucent fronds are ugly. By no means – they are works of art and a fine addition to any ecosystem. But they probably lack the mass appeal of NZ’s better known ferns so you’re unlikely to see them become a patented logo any time soon.

And by the way, in case you think they deserve a spot in your prized fernery back home – don’t bother – they are apparently very difficult to transplant or propagate. Best to just enjoy them in situ.

Adding to their distinctive appearance is the unusual placement of a feature that is typical of ferns – the sori. On Kidney ferns they are located around the edge of mature fronds, whereas on your your run-of-the-mill NZ fern, they are usually found on the underside of the frond.

These sori contain the sporangia where spores are formed and from whence they are dispensed. On the Kidney fern the sporangia are housed in the stalks clearly visible in the image of a mature Kidney fern frond below.

About the Kidney Fern – Hymenophyllum nephrophyllum

This fern is native to New Zealand and not likely to be confused with any other. Its unique shape sets it apart from other NZ ferns. Hymenophyllum nephrophyllum is a creeping fern that tends to form mats on tree trunks, rocks and on the ground. The shiny green fronds can be anything from around 17mm long x 25mm wide to 65mm x 105mm wide.¹

Nomenclature/Etymology

As seems to often be the case, the Kidney fern has cycled through several names before settling on Hymenophyllum nephrophyllum. This fern belongs to the Hymenophyllaceae ² family. The first part of the scientific name indicates the genus – Hymenophyllum.³ The second half is apparently derived from the Greek ‘nephro’ meaning ‘kidney-shaped’ and ‘phyllus’ meaning ‘leaved’ – a reference to the shape of the frond.⁴

Common names: kidney fern, raurenga, konehu, kopakopa.

Distribution and Habitat of the Kidney Fern

The Kidney fern can be found in Northland, Auckland, the Volcanic Plateau, Gisborne, Taranaki and the Southern North Island. On the mainland it’s found in the Marlborough Sounds, North-Western Nelson, Westland and Fiordland and southern Southland.⁵ Also the Chatham Islands and Stewart Island.

In terms of altitude they typically live between 10-780m – lowlands and mountainside forest ecosystems.⁶ As mentioned above, they tend to form mats on the forest floor, tree trunks, banks and rocky areas. They don’t transplant and are not commercially available due to the difficulty of propagation.

Click on the map to see a larger version of distribution data from Landcare Research.

You can also checkout inaturalist.org for distribution information, images and recent sightings.

Sources & further reading

• http://www.nzflora.info/factsheet/Taxon/Hymenophyllum-nephrophyllum.html
• http://nzpcn.org.nz/flora_details.aspx?ID=1322
• https://www.inaturalist.org/taxa/340730-Hymenophyllum-nephrophyllum
• http://www.nzplants.auckland.ac.nz/en/about/ferns/native-ferns/hymenophyllaceae-filmy-ferns/cardiomanes-reniforme-trichomanes-reniforme-hymenophyllum-neph.html
• https://maoriplantuse.landcareresearch.co.nz/WebForms/PeoplePlantsDetails.aspx?firstcome=firstcome&PKey=5F01CF55-4522-490C-BCAB-6414BA942108

1. Those figures from http://www.nzflora.info/factsheet/Taxon/Hymenophyllum-nephrophyllum.html. Other sources seem to vary in their numbers. Next time I’ll take a ruler.
2. cf. http://www.nzflora.info/factsheet/Taxon/Hymenophyllaceae.html
3. cf http://www.nzflora.info/factsheet/Taxon/Hymenophyllum.html
4. I’m completely ignorant of how botanical names are formed, but whereas those names may be derived from Greek, they certainly look like Latin in their form. Are they actual Latin words derived from Greek? Or are they Greek words adapted to create botanical nomenclature? Someone knows, but alas not I at this point.
5. cf http://www.nzflora.info/factsheet/Taxon/Hymenophyllum-nephrophyllum.html
6. According to http://www.nzflora.info/factsheet/Taxon/Hymenophyllum-nephrophyllum.html