A new scientific name for one of Aotearoa’s most common ferns, kōwaowao – again

A new scientific name for one of Aotearoa’s most common ferns, kōwaowao – again

Botany Curator Leon Perrie writes about why kōwaowao, hound’s tongue fern has had a scientific name change from Microsorum pustulatum to Lecanopteris pustulata.

New Zealanders will probably recognise kōwaowao. It is widespread, and the most commonly observed fern in Aotearoa New Zealand, based on iNaturalist records. It is distinctive, with its glossy green fronds spread along a creeping or climbing rhizome. But it is a fern of many, many names.

A single picture with four images of fern fronds and one map of New Zealand with dots showing distribution on all parts of the country
Kōwaowao, hound’s tongue fern, Lecanopteris pustulata; previously Microsorum pustulatum. Clockwise from top left: fertile frond; sterile fronds, with wider lobes; distribution map within New Zealand; creeping rhizome; underside of fertile frond, with prominent orange clusters of the spore-producing capsules. Photos by Leon Perrie, Te Papa. Distribution map by K.Boardman, Flora of New Zealand, 2021. CC BY 4.0, Landcare Research

A fern of many names

The Māori Dictionary says that the word kōwaowao is also used as a noun for “low vegetation”, and as a verb for “to overgrow”. Both of these other meanings reflect the fern’s propensity for carpeting the ground or tree trunks.

Other te reo Māori names for this fern include maratata, pāraha, pāraharaha, and raumanga, from the New Zealand Plant Names Database.

The colloquial English name in New Zealand is hound’s tongue. The unlobed fronds of young plants are somewhat tongue-shaped. But I haven’t seen many tongues lobed like the fern’s mature fronds.

This fern is also indigenous to eastern Australia, where it is called kangaroo fern. I don’t know why.

The earliest scientific name is Polypodium pustulatum, authored in 1786 by Georg Forster, who was a naturalist on Captain Cook’s second expedition into the Pacific. But species epithets of scandens, diversifolium, and billardierei have also been used for the second part of the two-part scientific name. And these species epithets have variously been combined with the generic names of Polypodium, Phymatosorus, Microsorum, Pleopeltis, Phymatodes, Chrysopteris, and Drynaria!

Even in just the last 35 years, kōwaowao has been known in New Zealand as Phymatosorus diversifolius, Phymatosorus pustulatus, Microsorum pustulatum, and, as outlined below, Zealandia pustulata and Lecanopteris pustulata.

This plethora of scientific names reflects uncertainty about (1) the correct species epithet (now seemingly settled as based on pustulatum), and (2) the most appropriate genus; more on this below.

Related New Zealanders

Kōwaowao has two indigenous relatives in Aotearoa. One looks very similar. It has no recorded te reo Māori or English name, but has been known as Microsorum novae-zealandiae. It’s endemic to New Zealand, being confined to middle and high elevation forests of the central and southern North Island.

A single picture with two images of fern fronds and one map of New Zealand with dots in the North Island
Lecanopteris novae-zealandiae; previously Microsorum novae-zealandiae. Fertile frond, with narrower lobes; rhizome with distinctive orange-brown scales; distribution map. Photos by Leon Perrie, Te Papa. Distribution map by K.Boardman, Flora of New Zealand, 2021. CC BY 4.0, Landcare Research

The third species has been called Microsorum scandens. It has a te reo Māori name of mokimoki, which is also used for a Blechnum fern in the Doodia group, and moki, like the fish. The colloquial English name is fragrant fern. I’ve a weak sense of smell, but apparently, it is musky and can be used to scent essential oil. Mokimoki isn’t as widespread as kōwaowao, being restricted to more sheltered habitats, but it is similarly also indigenous to eastern Australia. It is recognised by its dull, narrower fronds and narrow rhizomes.

A single picture with four images of fern fronds and one map of New Zealand with dots showing distribution on the North and South islands.
Mokimoki, fragrant fern, Lecanopteris scandens; previously Microsorum scandens. Clockwise from top left: fronds epiphytic on a tree trunk; underside of fertile frond, with small clusters of spore-producing capsules; distribution map within New Zealand; creeping rhizome; fronds carpeting the ground. Photos by Leon Perrie, Te Papa. Distribution map by K.Boardman, Flora of New Zealand, 2021. CC BY 4.0, Landcare Research

The problem with Microsorum

It’s been known since at least 2004 that the three New Zealand species are taxonomically misplaced in Microsorum. This is because they are not related to the name-bearing type species of Microsorum.

A single picture with a botanical tree structure on one part and then two images of fern fronds
Left: summary of the relationships among Microsorum and its relatives, including kōwaowao and mokimoki. Figure adapted from Perrie et al. (2021); Centre: Microsorum punctatum, the accepted name for the type species of Microsorum. The latter name needs to be applied to the lineage that includes this type species, which is here labelled ‘True’ Microsorum. Photo by twan3253 via iNaturalist, CC BY; Right: Microsorum grossum, which looks a lot like kōwaowao but actually belongs in the ‘true’ Microsorum lineage. Superficial appearances often do not reflect relationships in this wider group of ferns. Photo by Leon Perrie

Rather, the three New Zealand species fall into two lineages most closely-related to Lecanopteris. All 13 species of Lecanopteris (in its narrow sense) are associated with ants and most have hollow rhizomes in which ants live.

A single picture with two images of plants and two images of a cross-section of a branch with ants sitting inside the gap
Lecanopteris sinuosa, which has cavities within its rhizomes, in which ants live. Right: photo by Leon Perrie, Te Papa; Centre: photo by geechartier, via iNaturalist, CC BY; Left: photos by emdestigter, via iNaturalist, CC BY-NC

An Australian relative of the three New Zealand misplaced-in-Microsorum species is also associated with ants. That this is not the case here could be due to New Zealand being globally-depauperate in ants!

Alternative solutions

To have a scientific classification that reflects evolutionary relationships, the three New Zealand species, along with their immediate relatives, need to be shifted from Microsorum.

One solution is to recognise the lineages alongside Lecanopteris as separate genera.  In this case, the scientific names for the New Zealand species become Dendroconche scandens, Zealandia novae-zealandiae, and Zealandia pustulata. The genera Dendroconche and Zealandia are quite small with, respectively, eight and four species. With this scheme, additional small genera might be required depending on how present uncertainty about relationships is resolved.

Another solution is to expand the circumscription of Lecanopteris so that it encompasses the lineages including the three species in New Zealand. Their scientific names are then Lecanopteris novae-zealandiae, Lecanopteris pustulata, and Lecanopteris scandens.

An illustration of a comparison tree with scientific botanical text on each branch
Comparison of two taxonomic solutions for the species of the two lineages misplaced in Microsorum. Each lineage could be recognised as its own genus, or they could be incorporated into an expanded Lecanopteris. Figure adapted from Perrie et al. (2021)

This expanded Lecanopteris is characterised by a particular pattern of the frond veins and internal features of the rhizome. While it is otherwise morphologically diverse, so were several of the segregates. And superficial appearances have often proved to be poor indicators of evolutionary relationships with the broader family, the Polypodiaceae.

An advantage of the expanded Lecanopteris option is that it retains in one genus (i.e., Lecanopteris) species that have traditionally been in the same genus (e.g., Microsorum) rather than distributing them across different genera (i.e., Dendroconche and Zealandia). And we believe it does this without overly inconveniencing those already familiar with Lecanopteris, because of largely non-overlapping distributions.

Conclusions

We prefer the option of expanding Lecanopteris. We detail this in a recently published paper. We have also adopted it for the Flora of New Zealand.

While we want to use scientific names that reflect evolutionary relationships, we nevertheless recognise this may be a difficult change, not least with a group of ferns that has already experienced many name changes. That difficulty is at least a partial explanation of why it has taken us nearly 20 years to implement a taxonomic solution. We’ll understand if it is difficult to let go of Microsorum for kōwaowao and its relatives.

4 Comments

  1. Hi Leon, thanks I always enjoy reading the work you and the botany team are achieving in Te Papa. Have you and the team considered building a Coursera (https://www.coursera.org/) module on ferns or other NZ endemic species? It might be a great way to increase the reach for you, your team and Te Papa? Also, there is only a few botany focused courses in Coursera, so would be a great way to break through some ‘plant blindness’. Thanks again and all the best.

    1. Author

      Kia ora. Thanks for the suggestion. I’ll look into Coursea.
      In the meantime, I regularly teach in-person about fern identification, and am happy to do that to groups around the country. I’m working on a photo guide to New Zealand ferns and lycophytes. The lycophyte section is available here: https://www.tepapa.govt.nz/discover-collections/read-watch-play/ferns-and-lycophytes/guide-lycopodiaceae-new-zealand And I’ve drafts for tree ferns, the Blechnaceae, and Pteridaceae that I can send to anyone interested. The filmy ferns are next on my ‘to-do’ list.
      For a general overview of Aotearoa’s ferns, this presentation I gave recently to the Botanic Gardens in Melbourne may be of interest: https://drive.google.com/file/d/1vcZWDctD6eqpjnaqo2dOBOIXsUCBCekh/view

  2. Great work Leon. It’s clear you’ve put a lot of time into this.

    1. Author

      thanks David.

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