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 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.

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.

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.

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.

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.

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.

• Our open-access paper implementing the expansion of Lecanopteris.
• Flora of New Zealand chapter for the Polypodiaceae (9 MB pdf).

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.