A fern connection between New Zealand offshore islands and mountains of Borneo and New Guinea

A fern connection between New Zealand offshore islands and mountains of Borneo and New Guinea

Botany curator Leon Perrie describes how a New Zealand fern’s closest relative has turned up in an unexpected place.

The Poor Knights spleenwort, Asplenium pauperequitum, was scientifically described in 1984, led by Te Papa’s Pat Brownsey. At the time, it was thought confined to its eponymous island group off the east coast of Northland. It has not been found on the North or South Islands, but the Poor Knights spleenwort was subsequently found on the Chatham Islands, some 1200 km away!

Because it has only small populations, it has a conservation status of Nationally Endangered.

The Poor Knights spleenwort, Asplenium pauperequitum, on Chatham Island. Photo by Peter de Lange, CC0 1.0, via iNaturalist

Our DNA sequencing studies had shown that the Poor Knights spleenwort is not closely related to any of the other Asplenium species found in New Zealand, Australia, New Caledonia, or elsewhere in the Pacific.

So I was intrigued by a recent study (Xu et al. 2020, Cladistics 36: 22-71) that incidentally reported an unidentified sample collected from Borneo’s Mount Kinabalu as closely related to the Poor Knights spleenwort.

A distant connection

That Mount Kinabalu sample was collected by Cheng-Wei Chen. I knew Cheng-Wei from helping with his (excellent) book on the ferns of the Solomon Islands. He told me he had ruled out all spleenworts previously reported from Mount Kinabalu except for an unnamed species listed in a book by Barbara Parris.

Barbara is a New Zealander who was fern curator at the herbarium of Kew gardens. She has collected ferns on Mount Kinabalu among other places in south-east Asia.

I checked her specimens in the Kew collection, and with Barbara herself, and we confirmed that Barbara’s unnamed species was the same as Cheng-Wei’s specimen, for which DNA sequence data had been published.

Independently, Daniel Ohlsen found a specimen among the Papua New Guinean collections in the Canberra herbarium that resembled Asplenium pauperequitum. Guess what? Daniel’s find was the same species as Barbara and Cheng-Wei’s.

Cheng-Wei Chen’s collection of Asplenium alleniae from Mount Kinabalu. Photo courtesy of Cheng-Wei Chen, Herbarium of Taiwan Forestry Research Institute

A new species

Putting this all together, Barbara, Cheng-Wei, Daniel, Pat and I formally described this species with a new scientific name, Asplenium alleniae. Compared with the Poor Knights spleenwort, Asplenium alleniae has larger fronds with fewer pairs of pinnae (frond segments), and the pinnae are longer and have more pointed ends.

Asplenium alleniae is known only from Mount Kinabalu on Borneo and Mount Giluwe on New Guinea, at elevations between 3160 and 3500 m.

We suggested it be regarded as Endangered because of its limited populations and because tropical mountain habitats are considered particularly susceptible to global warming.

Despite the distance between them, Asplenium alleniae (grey diamonds) and Asplenium pauperequitum (black squares) are each other’s closest relative based on current data. Each comprises far-flung populations, suggestive of both habitat specialisation and an ability to disperse long distances. Image by Leon Perrie. Te Papa

Naming

Asplenium alleniae is named for Betty Molesworth Allen (1913–2002). She made the earliest scientific collection of the species that we know about. Betty spent most of her working career in south-east Asia, extensively collecting plants, particularly ferns, through Malaysia, Borneo, and Thailand. She was, however, born and brought up in New Zealand.

The scientific name of this species thus parallels the kinship link that this fern of tropical mountains in Borneo and New Guinea has with New Zealand.

Further reading

10 Comments

  1. Hi Leon,
    To your second posting: “our scenarios seem unlikely because it is very doubtful that these ferns are as old as you suggest.”

    It’s not doubtful for me.

    “I’ve seen molecular dating that suggests the family may be c. 190 million years (Testo & Sundue2016, Molecular Phylogenetics & Evolution), but others have suggested it is much more recent.”

    If these are fossil calibrated ages then they are minimum ages

    “With your vicariant Gondwanan scenario, a massive amount of evolutionary change has to be compressed into the time between the family’s origin and the break-up of the relevant parts of Gondwana, AND molecular (and morphological) evolution then has to slow dramatically, in parallel across multiple lineages.”

    Or it means that rates of evolution do actually vary over time within a lineage.

    “Or it means the family is actually much older, which would push older the origins of ferns and landplants themselves. Either would be extraordinary.”

    Perhaps, but varying rates of evolution would be the alternative possibility.

    “ ferns are well-known for being able to colonise even remote oceanic islands.”

    Many other organisms also colonise ‘remote’ oceanic islands. The key issue is under what circumstances this’ colonization’ took place. There is even evidence for colonization through vicariance for the biota of the Galapagos (Heads & Grehan2021).

    “What are the other species found only on the Poor Knights and the Chathams?”

    Reads Heads (2017) and also recent articles in the newsletters of the Otago Bot Soc and NZ Entomological Society. You need to be fully informed about biogeographic patterns in NZ and the region at the very least – regardless of your explanatory preference.

    “The proposed sequential colonisation of volcanic islands in the area of the Chathams since the Mesozoic presumably would have entailed many dispersals across short stretches of water. When does that begin to blur into accepting occasional dispersals across medium-distances of water, or rare dispersals across long distances? Or is there an arbitrary distance that has to be considered impossible?”

    No, of course not. The issue at hand is the nature of allopatry and tectonic correlation. The allopatry of Chatham Islands endemics is consistent with sequential dispersal being local rather than involving the mainland of NZ or other regions where sister taxa occur (e.g. for Gallirallus birds where the Chathams sister group extends between NZ and Taiwan).

  2. Hi Leon,

    Somehow I was never notified of your comments, only brought to my attention now. Some comments below

    “I personally found parts of it incoherent, and many of its conclusions dubious.”

    Would have to have specifics to comment.

    “For me, the main problem is that panbiogeography seemingly has no way of testing whether a disjunction might be due to long-distance dispersal or vicariance.”

    This idea of ‘testing’ is often seen as some kind of ultimate authority that discerns one from the other. This is problematic as it first presupposes that allopatry can be the result of chance dispersal (panbiogeography accepts ecological dispersal as an emperical phenomenon) and that it is somehow possible to identify that process in given distributions and taxa. Ironically, you seem to have overlooked Craw’s (1987 [or 88] paper showiong how clique analysis could provide evidence of one or the other].

    “Rather, in effect it dismisses the possibility of long-distance dispersal”

    That boggles the mind. There are plenty examples of long distance dispersal of species in all sorts of taxa.

    “forced to adopt a vicariant explanation”

    no one is forced to adopt anything.

    “which often have to be relatively ancient to fit with known geological history (as is the case where connections between New Zealand and elsewhere are involved).”

    What is the emperical problem with that?

    “I’ve learnt to be wary of those who dogmatically attribute pretty much everything to the distant past, as if nothing meaningful has happened recently.”

    Sure – but what is ‘distant’ past vis ‘recently? If you read Heads’ (2017) book on NZ biogeography you will see a range of divergence ages for various groups, some more recent that others.

    “From what I understand of evolutionary rates and geological history, I’m very confident that long-distance dispersal does occur, at least rarely, and in at least some groups of organisms.”

    OK but would need precise examples to comment.

    “ think paradigms along the lines of Crisp & Cook (2007, A congruent molecular signature of vicariance across multiple lineages, Molecular Phylogenetics & Evolution, 43, 1106-1117) to be more scientifically appropriate for exploring biogeographic patterns.”

    In what way?

    “ Others might find the reviews by Waters et al. (2013, Biogeography off the tracks, Systematic Biology 62: 494-498) and McGlone (2016, Once more into the wilderness of panbiogeography, Australian Systematic Botany, 28: 388-393) of interest. I can email pdfs.”

    you really should read Heads (2015) Panbiogeography, its critics, and the case of the ratite birds. Australian Systematic Botany, 27, 241–256. I assume that by drawing attention to Waters et al you have no problem with their call for editorial censorship.

    “I’d be interested if you could share examples of where panbiogeography has inferred long-distance dispersal as an explanation for a disjunction. Otherwise, it’s unlikely you’ll change my mind about panbiogeography.”

    I’d like to see evidence for chance dispersal as the mechanism for a disjunction. That’s the primary problem for me. With your fern example I pointed out how the pattern was biogeographically congurent with other taxa, and that it was consistent with vicariance. If you have evidence of something else that would be of interest.

    Kind regards,

    John

  3. Kia ora anō John,
    I am suspecting your suggestions accord with the tenets of panbiogeography. I came across this research paradigm during postgraduate study. I like to think I explored it with an open mind (that was the learning environment), but in among some useful aspects, I personally found parts of it incoherent, and many of its conclusions dubious.

    For me, the main problem is that panbiogeography seemingly has no way of testing whether a disjunction might be due to long-distance dispersal or vicariance. Rather, in effect it dismisses the possibility of long-distance dispersal, and so is forced to adopt a vicariant explanation, which often have to be relatively ancient to fit with known geological history (as is the case where connections between New Zealand and elsewhere are involved). I’ve learnt to be wary of those who dogmatically attribute pretty much everything to the distant past, as if nothing meaningful has happened recently.

    From what I understand of evolutionary rates and geological history, I’m very confident that long-distance dispersal does occur, at least rarely, and in at least some groups of organisms. Consequently, I think paradigms along the lines of Crisp & Cook (2007, A congruent molecular signature of vicariance across multiple lineages, Molecular Phylogenetics & Evolution, 43, 1106-1117) to be more scientifically appropriate for exploring biogeographic patterns.

    Panbiogeography was apparently big in New Zealand before my time, but seems to have faded away. Others might find the reviews by Waters et al. (2013, Biogeography off the tracks, Systematic Biology 62: 494-498) and McGlone (2016, Once more into the wilderness of panbiogeography, Australian Systematic Botany, 28: 388-393) of interest. I can email pdfs.

    I’d be interested if you could share examples of where panbiogeography has inferred long-distance dispersal as an explanation for a disjunction. Otherwise, it’s unlikely you’ll change my mind about panbiogeography. Others will be interested in the diversity of opinions, and I’ll be happy to repeat mine about the weaknesses of the panbiogoegraphic approach.

    Crisp & Cook: https://www.sciencedirect.com/science/article/abs/pii/S1055790307000656

    Waters et al.: https://academic.oup.com/sysbio/article/62/3/494/1653732

    McGlone: https://www.publish.csiro.au/SB/SB15047

  4. Kia ora John,
    Your scenarios seem unlikely because it is very doubtful that these ferns are as old as you suggest. Asplenium alleniae and Asplenium pauperequitum constitute just a tiny fraction of the evolutionary diversity within Aspleniaceae (see Xu et al. 2019, Cladistics). I’ve seen molecular dating that suggests the family may be c. 190 million years (Testo & Sundue 2016, Molecular Phylogenetics & Evolution), but others have suggested it is much more recent. With your vicariant Gondwanan scenario, a massive amount of evolutionary change has to be compressed into the time between the family’s origin and the break-up of the relevant parts of Gondwana, AND molecular (and morphological) evolution then has to slow dramatically, in parallel across multiple lineages. Or it means the family is actually much older, which would push older the origins of ferns and land plants themselves. Either would be extraordinary. If you think you have the evidence to support your suggestions, I urge you to write a paper for the peer-reviewed literature, because the implications are enormous. On the other hand, with their tiny, wind-blown spores, ferns are well-known for being able to colonise even remote oceanic islands.

    What are the other species found only on the Poor Knights and the Chathams? Given NZ is home to tens of thousands of species, I wouldn’t be surprised if there were a few others, and I’d be pleased to know of them. Keep in mind that common ecologies are an explanation additional to shared geological histories for disjunctions that are shared by species.

    The proposed sequential colonisation of volcanic islands in the area of the Chathams since the Mesozoic presumably would have entailed many dispersals across short stretches of water. When does that begin to blur into accepting occasional dispersals across medium-distances of water, or rare dispersals across long distances? Or is there an arbitrary distance that has to be considered impossible?

  5. Comment on the statement that “Each comprises far-flung populations, suggestive of both habitat specialisation and an ability to disperse long distances” – this does not explain the allopatry of the two species. If it were so easy, why the allopatric differentiation. I suggest that the ability to disperse is an assumption that may not apply in terms of understanding the distribution. if so easy to disperse, then why just Poor Knights and Chathams? And why this particular pattern that is correlated with other animal and plant taxa? The distribution of the two species is consistent with a widespread ancestor along the East Gondwana coastline that was initially disrupted between NZ and NG. The NZ range is no greater than many other species, just noticeably disjunct. The Chathams population could represent persistence since the Mesozoic by sequential colonization of volcanic islands in the area through the Cenozoic.

  6. Great story Leon. I read the paper and see the scales on A. alleniae and A. pauperequitum (drawn in the 1984 paper) look very similar too.

    David Hutchinson.

    1. Author

      thanks David.

  7. I have just started reading Te Papa blog and find it very interesting. As a retired nature conservancy officer I’m now using the short summers here in the northernmost Scandinavia for flora registrations,

    Maybe you know Sofia Lund, who has been active in New Zealand some years ago. dealing with grasses and sedges. She has recently become the new red list responsible person in Sweden,

    Yours Mats Nettelbladt, mndt@online.no

    1. Author

      Kia ora Mats. Thanks for the interest. I’m afraid I don’t know Sofia, but grasses and sedges are not strong parts of my botany. Kind regards, Leon

  8. The assertion that “Each comprises far-flung populations, suggestive of both habitat specialisation and an ability to disperse long distances” does not explain the allopatry between the two, or that the NZ species links the Poor Knights and the Chathams. The allopatry is consistent with a vicariance origin of a widespread ancestor that ranged between S East Asia and NZ, perhaps along the Gondwana coastline. This would make sense of the allopatry and also the Poor Knights-Chathams connection that is seen in other taxa. The montane distributions in NG and Borneo could be the result of tecotnic uplift while the NZ species has retained its lowland/coastal range, with the Chathams population surviving locally since the Mesozoic by sequential colonization of volcanic islands in the region.

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